create mem/ subdir for all arena code

PiperOrigin-RevId: 485884460
diff --git a/BUILD b/BUILD
index ebf5139..705e28a 100644
--- a/BUILD
+++ b/BUILD
@@ -109,8 +109,6 @@
 cc_library(
     name = "upb",
     srcs = [
-        "upb/alloc.c",
-        "upb/arena.c",
         "upb/array.c",
         "upb/decode.c",
         "upb/encode.c",
@@ -130,6 +128,8 @@
         "upb/decode.h",
         "upb/encode.h",
         "upb/extension_registry.h",
+        "upb/mem/alloc.h",
+        "upb/mem/arena.h",
         "upb/message_value.h",
         "upb/msg.h",
         "upb/status.h",
@@ -140,12 +140,12 @@
     copts = UPB_DEFAULT_COPTS,
     visibility = ["//visibility:public"],
     deps = [
-        ":arena_internal",
         ":array_internal",
         ":decode_internal",
         ":encode_internal",
         ":extension_registry",
         ":fastdecode",
+        ":mem",
         ":port",
         ":table_internal",
         ":unicode_internal",
@@ -287,10 +287,10 @@
     ],
     copts = UPB_DEFAULT_COPTS,
     deps = [
-        ":arena_internal",
         ":array_internal",
         ":decode_internal",
         ":extension_registry",
+        ":mem_internal",
         ":port",
         ":table_internal",
     ],
@@ -944,8 +944,6 @@
 cc_library(
     name = "array_internal",
     srcs = [
-        "upb/alloc.h",
-        "upb/arena.h",
         "upb/array.h",
         "upb/internal/array.c",
         "upb/message_value.h",
@@ -958,25 +956,39 @@
     copts = UPB_DEFAULT_COPTS,
     visibility = ["//:__subpackages__"],
     deps = [
+        ":mem",
         ":port",
     ],
 )
 
 cc_library(
-    name = "arena_internal",
+    name = "mem",
     srcs = [
-        "upb/alloc.h",
-        "upb/arena.h",
+        "upb/mem/alloc.c",
+        "upb/mem/arena.c",
+        "upb/mem/arena_internal.h",
     ],
-    hdrs = ["upb/internal/arena.h"],
-    aspect_hints = [":suppress_kotlin_interop"],
-    compatible_with = ["//buildenv/target:non_prod"],
+    hdrs = [
+        "upb/mem/alloc.h",
+        "upb/mem/arena.h",
+    ],
     copts = UPB_DEFAULT_COPTS,
     visibility = ["//:__subpackages__"],
     deps = [":port"],
 )
 
 cc_library(
+    name = "mem_internal",
+    hdrs = ["upb/mem/arena_internal.h"],
+    copts = UPB_DEFAULT_COPTS,
+    visibility = ["//:__subpackages__"],
+    deps = [
+        ":mem",
+        ":port",
+    ],
+)
+
+cc_library(
     name = "atoi_internal",
     srcs = ["upb/internal/atoi.c"],
     hdrs = ["upb/internal/atoi.h"],
@@ -999,7 +1011,7 @@
     copts = UPB_DEFAULT_COPTS,
     visibility = ["//:__subpackages__"],
     deps = [
-        ":arena_internal",
+        ":mem_internal",
         ":port",
         ":table_internal",
         "//third_party/utf8_range",
@@ -1022,9 +1034,9 @@
         "upb/internal/table.c",
     ],
     hdrs = [
-        "upb/alloc.h",
-        "upb/arena.h",
         "upb/internal/table.h",
+        "upb/mem/alloc.h",
+        "upb/mem/arena.h",
         "upb/status.h",
         "upb/string_view.h",
         "upb/upb.h",
@@ -1058,7 +1070,6 @@
         "upb.h",
     ],
     libs = [
-        ":arena_internal",
         ":array_internal",
         ":atoi_internal",
         ":collections",
@@ -1067,6 +1078,8 @@
         ":encode_internal",
         ":extension_registry",
         ":fastdecode",
+        ":mem",
+        ":mem_internal",
         ":mini_table",
         ":port",
         ":reflection",
@@ -1091,7 +1104,6 @@
         "php-upb.h",
     ],
     libs = [
-        ":arena_internal",
         ":array_internal",
         ":atoi_internal",
         ":collections",
@@ -1102,6 +1114,8 @@
         ":extension_registry",
         ":fastdecode",
         ":json",
+        ":mem",
+        ":mem_internal",
         ":mini_table",
         ":port",
         ":reflection",
@@ -1130,7 +1144,6 @@
         "ruby-upb.h",
     ],
     libs = [
-        ":arena_internal",
         ":array_internal",
         ":atoi_internal",
         ":collections",
@@ -1140,6 +1153,8 @@
         ":extension_registry",
         ":fastdecode",
         ":json",
+        ":mem",
+        ":mem_internal",
         ":mini_table",
         ":port",
         ":reflection",