Port of the interesting `GPBUnknownFieldsSet` tests to `GPBUnknownFields`
as they provide coverage of general handing of unknown fields during parsing.
Also tweak the `Set` tests to actually use a registry to confirm behaviors around
extensions where the test previously wasn't as complete.
PiperOrigin-RevId: 650660181
VLAs complicate static analysis and bloat stack size. Replace VLA allocation
with calls to malloc and free. This will alos the code to build with -Wvla.
- Correct some cases sources were compiled into the static lib and the tests.
- Enable Xcodes code coverage support on the unittests. We aren't complete on
coverage, but having the data always there should make it easier to chip away
at this going forward.
- Drop method in tests that isn't used, wire up a validator in another test.
- Add more to the ObjC dir readme.
- Merge the ExtensionField and ExtensionDescriptor to reduce overhead.
- Fix an initialization race.
- Clean up the Xcode schemes.
- Remove the class/enum filter.
- Remove some forced inline that were bloating things without proof of performance wins.
- Rename some internal types to avoid conflicts with the well know types protos.
- Drop the use of ApplyFunctions to the compiler/optimizer can do what it wants.
- Better document some possible future improvements.
- Add missing support for parsing repeated primitive fields in packed or unpacked forms.
- Improve -hash.
- Add *Count for repeated and map<> fields to avoid auto create when checking for them being set.
- Style fixups in the code.
- map<> serialization fixes and more tests.
- Autocreation of map<> fields (to match repeated fields).
- @@protoc_insertion_point(global_scope|imports).
- Fixup proto2 syntax extension support.
- Move all startup code to +initialize so it happen on class usage and not app startup.
- Have generated headers use forward declarations and move imports into generated code, reduces what is need at compile time to speed up compiled and avoid pointless rippling of rebuilds.