Prepare to reorganize upb file structure

I am getting ready to move almost everything under the upb/ directory up one
level to integrate upb better into its new location in the protobuf repo. This
change makes a few tweaks to prepare for that:
- Delete upb's LICENSE and CONTRIBUTING.md files since we already have similar
  files at the top level.
- Rename `//python:python_version` so that it won't conflict later with
  `//upb/python:python_version`.
- Move the contents of python/BUILD.bazel out to a Bazel macro to facilitate
  merging that BUILD.bazel file with upb/python/BUILD.

PiperOrigin-RevId: 567119840
diff --git a/python/build_targets.bzl b/python/build_targets.bzl
new file mode 100644
index 0000000..546ef01
--- /dev/null
+++ b/python/build_targets.bzl
@@ -0,0 +1,474 @@
+# Protobuf Python runtime
+#
+# See also code generation logic under /src/google/protobuf/compiler/python.
+#
+# Most users should depend upon public aliases in the root:
+#   //:protobuf_python
+#   //:well_known_types_py_pb2
+
+load("@rules_pkg//:mappings.bzl", "pkg_files", "strip_prefix")
+load("@rules_python//python:defs.bzl", "py_library")
+load("//:protobuf.bzl", "internal_py_proto_library")
+load("//build_defs:arch_tests.bzl", "aarch64_test", "x86_64_test")
+load("//build_defs:cpp_opts.bzl", "COPTS")
+load("//conformance:defs.bzl", "conformance_test")
+load(":internal.bzl", "internal_copy_files", "internal_py_test")
+
+def build_targets(name):
+    """
+    Declares the build targets of the //python package.
+
+    Args:
+      name: unused.
+    """
+    py_library(
+        name = "protobuf_python",
+        data = select({
+            "//conditions:default": [],
+            ":use_fast_cpp_protos": [
+                ":google/protobuf/internal/_api_implementation.so",
+                ":google/protobuf/pyext/_message.so",
+            ],
+        }),
+        visibility = ["//:__pkg__"],
+        deps = [
+            ":python_srcs",
+            ":well_known_types_py_pb2",
+        ],
+    )
+
+    native.config_setting(
+        name = "use_fast_cpp_protos",
+        values = {
+            "define": "use_fast_cpp_protos=true",
+        },
+    )
+
+    internal_py_proto_library(
+        name = "well_known_types_py_pb2",
+        srcs = [":copied_wkt_proto_files"],
+        include = ".",
+        default_runtime = "",
+        protoc = "//:protoc",
+        srcs_version = "PY2AND3",
+        visibility = [
+            "//:__pkg__",
+            "//upb:__subpackages__",
+        ],
+    )
+
+    internal_copy_files(
+        name = "copied_wkt_proto_files",
+        srcs = [
+            "//:well_known_type_protos",
+            "//src/google/protobuf:descriptor_proto_srcs",
+            "//src/google/protobuf/compiler:plugin.proto",
+        ],
+        strip_prefix = "src",
+    )
+
+    native.cc_binary(
+        name = "google/protobuf/internal/_api_implementation.so",
+        srcs = ["google/protobuf/internal/api_implementation.cc"],
+        copts = COPTS + [
+            "-DPYTHON_PROTO2_CPP_IMPL_V2",
+        ],
+        linkshared = 1,
+        linkstatic = 1,
+        tags = [
+            # Exclude this target from wildcard expansion (//...) because it may
+            # not even be buildable. It will be built if it is needed according
+            # to :use_fast_cpp_protos.
+            # https://docs.bazel.build/versions/master/be/common-definitions.html#common-attributes
+            "manual",
+        ],
+        deps = select({
+            "//conditions:default": [],
+            ":use_fast_cpp_protos": ["//external:python_headers"],
+        }),
+    )
+
+    native.config_setting(
+        name = "allow_oversize_protos",
+        values = {
+            "define": "allow_oversize_protos=true",
+        },
+    )
+
+    native.cc_binary(
+        name = "google/protobuf/pyext/_message.so",
+        srcs = native.glob([
+            "google/protobuf/pyext/*.cc",
+            "google/protobuf/pyext/*.h",
+        ]),
+        copts = COPTS + [
+            "-DGOOGLE_PROTOBUF_HAS_ONEOF=1",
+        ] + select({
+            "//conditions:default": [],
+            ":allow_oversize_protos": ["-DPROTOBUF_PYTHON_ALLOW_OVERSIZE_PROTOS=1"],
+        }),
+        includes = ["."],
+        linkshared = 1,
+        linkstatic = 1,
+        tags = [
+            # Exclude this target from wildcard expansion (//...) because it may
+            # not even be buildable. It will be built if it is needed according
+            # to :use_fast_cpp_protos.
+            # https://docs.bazel.build/versions/master/be/common-definitions.html#common-attributes
+            "manual",
+        ],
+        deps = [
+            ":proto_api",
+            "//:protobuf",
+            "//src/google/protobuf:descriptor_legacy",
+        ] + select({
+            "//conditions:default": [],
+            ":use_fast_cpp_protos": ["//external:python_headers"],
+        }),
+    )
+
+    aarch64_test(
+        name = "aarch64_test",
+        bazel_binaries = [
+            "google/protobuf/internal/_api_implementation.so",
+            "google/protobuf/pyext/_message.so",
+        ],
+    )
+
+    x86_64_test(
+        name = "x86_64_test",
+        bazel_binaries = [
+            "google/protobuf/internal/_api_implementation.so",
+            "google/protobuf/pyext/_message.so",
+        ],
+    )
+
+    py_library(
+        name = "python_srcs",
+        srcs = native.glob(
+            [
+                "google/protobuf/**/*.py",
+            ],
+            exclude = [
+                "google/protobuf/internal/*_test.py",
+                "google/protobuf/internal/test_util.py",
+                "google/protobuf/internal/import_test_package/__init__.py",
+            ],
+        ),
+        imports = ["python"],
+        srcs_version = "PY2AND3",
+        visibility = [
+            "//:__pkg__",
+            "//upb:__subpackages__",
+        ],
+    )
+
+    py_library(
+        name = "python_test_srcs",
+        srcs = native.glob([
+            "google/protobuf/internal/*_test.py",
+        ]) + [
+            "google/protobuf/internal/import_test_package/__init__.py",
+            "google/protobuf/internal/test_util.py",
+            "//python/google/protobuf/internal/numpy:__init__.py",
+            "//python/google/protobuf/internal/numpy:numpy_test.py",
+        ],
+        imports = ["python"],
+        srcs_version = "PY3",
+        visibility = [
+            "//:__pkg__",
+            "//upb:__subpackages__",
+        ],
+    )
+
+    ################################################################################
+    # Tests
+    ################################################################################
+
+    internal_copy_files(
+        name = "copied_test_proto_files",
+        testonly = 1,
+        srcs = [
+            "//:test_proto_srcs",
+            "//src/google/protobuf/util:test_proto_srcs",
+        ],
+        strip_prefix = "src",
+    )
+
+    internal_copy_files(
+        name = "copied_test_messages_proto2_files",
+        testonly = 1,
+        srcs = [
+            "//src/google/protobuf:test_messages_proto2.proto",
+        ],
+        strip_prefix = "src",
+    )
+
+    internal_copy_files(
+        name = "copied_test_messages_proto3_files",
+        testonly = 1,
+        srcs = [
+            "//src/google/protobuf:test_messages_proto3.proto",
+        ],
+        strip_prefix = "src",
+    )
+
+    internal_py_proto_library(
+        name = "python_common_test_protos",
+        testonly = 1,
+        srcs = [":copied_test_proto_files"],
+        include = ".",
+        default_runtime = "",
+        protoc = "//:protoc",
+        srcs_version = "PY2AND3",
+        visibility = ["//:__pkg__"],
+        deps = [":well_known_types_py_pb2"],
+    )
+
+    internal_py_proto_library(
+        name = "python_specific_test_protos",
+        testonly = 1,
+        srcs = native.glob([
+            "google/protobuf/internal/*.proto",
+            "google/protobuf/internal/import_test_package/*.proto",
+        ]),
+        include = ".",
+        default_runtime = ":protobuf_python",
+        protoc = "//:protoc",
+        srcs_version = "PY2AND3",
+        visibility = ["//:__pkg__"],
+        deps = [":python_common_test_protos"],
+    )
+
+    internal_py_proto_library(
+        name = "test_messages_proto2_py_proto",
+        testonly = 1,
+        srcs = [":copied_test_messages_proto2_files"],
+        include = ".",
+        default_runtime = "//:protobuf_python",
+        protoc = "//:protoc",
+        visibility = [
+            "//conformance:__pkg__",
+            "//python:__subpackages__",
+        ],
+    )
+
+    internal_py_proto_library(
+        name = "test_messages_proto3_py_proto",
+        testonly = 1,
+        srcs = [":copied_test_messages_proto3_files"],
+        include = ".",
+        default_runtime = "//:protobuf_python",
+        protoc = "//:protoc",
+        visibility = [
+            "//conformance:__pkg__",
+            "//python:__subpackages__",
+        ],
+        deps = [":well_known_types_py_pb2"],
+    )
+
+    py_library(
+        name = "python_test_lib",
+        testonly = 1,
+        srcs = [
+            "google/protobuf/internal/import_test_package/__init__.py",
+            "google/protobuf/internal/test_util.py",
+        ],
+        imports = ["python"],
+        srcs_version = "PY2AND3",
+        visibility = ["//python:__subpackages__"],
+        deps = [
+            ":protobuf_python",
+            ":python_common_test_protos",
+            ":python_specific_test_protos",
+        ],
+    )
+
+    internal_py_test(
+        name = "descriptor_database_test",
+        srcs = ["google/protobuf/internal/descriptor_database_test.py"],
+    )
+
+    internal_py_test(
+        name = "descriptor_pool_test",
+        srcs = ["google/protobuf/internal/descriptor_pool_test.py"],
+    )
+
+    internal_py_test(
+        name = "descriptor_test",
+        srcs = ["google/protobuf/internal/descriptor_test.py"],
+    )
+
+    internal_py_test(
+        name = "field_mask_test",
+        srcs = ["google/protobuf/internal/field_mask_test.py"],
+    )
+
+    internal_py_test(
+        name = "generator_test",
+        srcs = ["google/protobuf/internal/generator_test.py"],
+    )
+
+    internal_py_test(
+        name = "import_test",
+        srcs = ["google/protobuf/internal/import_test.py"],
+    )
+
+    internal_py_test(
+        name = "json_format_test",
+        srcs = ["google/protobuf/internal/json_format_test.py"],
+    )
+
+    internal_py_test(
+        name = "keywords_test",
+        srcs = ["google/protobuf/internal/keywords_test.py"],
+    )
+
+    internal_py_test(
+        name = "message_factory_test",
+        srcs = ["google/protobuf/internal/message_factory_test.py"],
+    )
+
+    internal_py_test(
+        name = "message_test",
+        srcs = ["google/protobuf/internal/message_test.py"],
+        data = ["//src/google/protobuf:testdata"],
+    )
+
+    internal_py_test(
+        name = "proto_builder_test",
+        srcs = ["google/protobuf/internal/proto_builder_test.py"],
+    )
+
+    internal_py_test(
+        name = "reflection_test",
+        srcs = ["google/protobuf/internal/reflection_test.py"],
+    )
+
+    internal_py_test(
+        name = "service_reflection_test",
+        srcs = ["google/protobuf/internal/service_reflection_test.py"],
+    )
+
+    internal_py_test(
+        name = "symbol_database_test",
+        srcs = ["google/protobuf/internal/symbol_database_test.py"],
+    )
+
+    internal_py_test(
+        name = "text_encoding_test",
+        srcs = ["google/protobuf/internal/text_encoding_test.py"],
+    )
+
+    internal_py_test(
+        name = "text_format_test",
+        srcs = ["google/protobuf/internal/text_format_test.py"],
+        data = ["//src/google/protobuf:testdata"],
+    )
+
+    internal_py_test(
+        name = "unknown_fields_test",
+        srcs = ["google/protobuf/internal/unknown_fields_test.py"],
+    )
+
+    internal_py_test(
+        name = "well_known_types_test",
+        srcs = ["google/protobuf/internal/well_known_types_test.py"],
+    )
+
+    internal_py_test(
+        name = "wire_format_test",
+        srcs = ["google/protobuf/internal/wire_format_test.py"],
+    )
+
+    native.cc_library(
+        name = "proto_api",
+        hdrs = ["google/protobuf/proto_api.h"],
+        visibility = ["//visibility:public"],
+        deps = [
+            "//external:python_headers",
+        ],
+    )
+
+    internal_py_test(
+        name = "python_version_test",
+        srcs = ["python_version_test.py"],
+    )
+
+    conformance_test(
+        name = "conformance_test",
+        env = {"PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION": "python"},
+        failure_list = "//conformance:failure_list_python.txt",
+        target_compatible_with = select({
+            "@system_python//:none": ["@platforms//:incompatible"],
+            ":use_fast_cpp_protos": ["@platforms//:incompatible"],
+            "//conditions:default": [],
+        }),
+        testee = "//conformance:conformance_python",
+        text_format_failure_list = "//conformance:text_format_failure_list_python.txt",
+    )
+
+    # Note: this requires --define=use_fast_cpp_protos=true
+    conformance_test(
+        name = "conformance_test_cpp",
+        env = {"PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION": "cpp"},
+        failure_list = "//conformance:failure_list_python.txt",
+        target_compatible_with = select({
+            "@system_python//:none": ["@platforms//:incompatible"],
+            ":use_fast_cpp_protos": [],
+            "//conditions:default": ["@platforms//:incompatible"],
+        }),
+        testee = "//conformance:conformance_python",
+        text_format_failure_list = "//conformance:text_format_failure_list_python_cpp.txt",
+    )
+
+    ################################################################################
+    # Distribution files
+    ################################################################################
+
+    pkg_files(
+        name = "python_source_files",
+        srcs = native.glob(
+            [
+                "google/protobuf/**/*.py",
+            ],
+            exclude = [
+                "google/protobuf/internal/*_test.py",
+                "google/protobuf/internal/test_util.py",
+                "google/protobuf/internal/import_test_package/__init__.py",
+            ],
+        ) + [
+            "README.md",
+            "google/__init__.py",
+            "setup.cfg",
+            "tox.ini",
+        ],
+        strip_prefix = "",
+        visibility = ["//upb:__subpackages__"],
+    )
+
+    pkg_files(
+        name = "dist_files",
+        srcs = native.glob([
+            "google/**/*.proto",
+            "google/**/*.py",
+            "google/protobuf/internal/*.cc",
+            "google/protobuf/pyext/*.cc",
+            "google/protobuf/pyext/*.h",
+        ]) + [
+            "BUILD.bazel",
+            "MANIFEST.in",
+            "README.md",
+            "google/protobuf/proto_api.h",
+            "google/protobuf/pyext/README",
+            "google/protobuf/python_protobuf.h",
+            "internal.bzl",
+            "python_version_test.py",
+            "release.sh",
+            "setup.cfg",
+            "setup.py",
+            "tox.ini",
+        ],
+        strip_prefix = strip_prefix.from_root(""),
+        visibility = ["//pkg:__pkg__"],
+    )