1. `for x in mapping` now yields keys rather than values, to match Python conventions and the behavior of the old library.
2. Lookup operations now correctly reject unhashable types as map keys.
3. We implement `repr()` to use the same format as `dict`
PiperOrigin-RevId: 459491734
Lots of changes but it's all just moving things around.
Backward-compatible stub #include's have been provided for now.
upb_Arena/upb_Status have been split out from upb/upb.?
upb_Array/upb_Map/upb_MessageValue have been split out from upb/collections.?
upb_ExtensionRegistry has been split out from upb/msg.?
upb/decode_internal.h is now upb/internal/decode.h
upb/mini_table_accessors_internal.h is now upb/internal/mini_table_accessors.h
upb/table_internal.h is now upb/internal/table.h
upb/upb_internal.h is now upb/internal/upb.h
PiperOrigin-RevId: 456297617
* Fixed some reference leaks.
* Fixed a few reference leaks.
* Fixed a few more memory errors.
* Fixed a few more reference leaks.
* Revert minimal_test.py.
* Re-enable limited API.
* Removed some debugging and spurious changes.
* Addressed PR comments.