Implement Editions in Pure Python.

This change only covers pure python, and follow-up changes will handle C++/upb variants and actually enable editions support.  The C++ one works (as evident from the conformance tests), but needs some APIs added to allow for testing.

PiperOrigin-RevId: 580304039

conformance/failure_list_python_cpp.txt

diff --git a/conformance/failure_list_python_cpp.txt b/conformance/failure_list_python_cpp.txt
index a499393..9b0dea6 100644
--- a/conformance/failure_list_python_cpp.txt
+++ b/conformance/failure_list_python_cpp.txt
@@ -9,3 +9,6 @@
 Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
 Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInOptionalField.ProtobufOutput
 Recommended.Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput
+Recommended.Editions_Proto3.JsonInput.IgnoreUnknownEnumStringValueInMapValue.ProtobufOutput
+Recommended.Editions_Proto3.JsonInput.IgnoreUnknownEnumStringValueInOptionalField.ProtobufOutput
+Recommended.Editions_Proto3.JsonInput.IgnoreUnknownEnumStringValueInRepeatedField.ProtobufOutput