MixPad

What's new in this version:

Compiler:
- Implement a retain_options flag in protoc
- Make protoc --descriptor_set_out respect option retention
- Modify release artifacts for protoc to statically link system libraries
- Extension declaration: Enforce that if the extension range has a declaration then all extensions in that range must be declared. This should prevent non-declared extensions from being added.
- Implement "reserved" for extension declaration
- Open-source extension declaration definition

C++:
- Fix(libprotoc): export useful symbols from .so
- Turn off clang::musttail on i386
- Fixes Clang 6 linker bug
- Remove PROTOBUF_DEPRECATED in favor of [[deprecated]]
- Add assert to the list of keywords for C++
- Added Reflection::GetCord() method in C++
- Support C++ protobuf ctype=CORD for bytes field
- Expand LazySerializerEmitter to cover proto3 cases
- Unconditionally generate unknown field accessors
- Introduce proto filter for inject_field_listener_events
- Add ParseFromCord to TextFormat
- Mark proto2::Arena::GetArena as deprecated

Java:
- Adds Timestamps.now()
- Added Reflection::GetCord() method in C++
- Re-attach OSGI headers to lite,core, and util. This information was dropped in the move from maven to bazel.
- Add Java FileDescriptor.copyHeadingTo() which copies file-level settingspackage, file options) to FileDescriptorProto.Builder
- Remove unnecessary has bits from proto2 Java
- Add casts to make protobuf compatible with Java 1.8 runtime
- Fix mutability bug in Java proto lite: sub-messages inside of oneofs were not
- Document known quirks of EnumDescriptor::is_closed() when importing across files with different syntaxes

Kotlin:
- Remove errorprone dependency from kotlin protos

Csharp:
- Make json_name take priority over name
- Add C# presence methods to proto3 oneof fields

Objective-C:
- Enforce the max message size when serializing to binary form
- Mark mergeFromData:extensionRegistry: as deprecated

Python:
- Fix bug in _internal_copy_files where the rule would fail in downstream repositories.
- Make numpy/pip_deps a test-only dependency.
- Fix Python bug with required fields
- Mark deprecated SupportsUnknownEnumValues on Message reflection. Use FieldDescriptor or EnumDescriptor instead.
- Raise warnings for MessageFactory class usages
- Add Python support for retention attribute
- Document known quirks of EnumDescriptor::is_closed() when importing across files with different syntaxes

Python C-Extension:
- Fix Python bug with required fields
- See also UPB changes below, which may affect Python C-Extension

PHP:
- RepeatedField: unset by index

PHP C-Extension:
- RepeatedField: unset by index
- See also UPB changes below, which may affect PHP C-Extension

Ruby:
- Change the Ruby code generator to emit a serialized proto instead of the DSL
- Feat(6178): emit ruby enum as integer

Ruby C-Extension:
- Feat(6178): emit ruby enum as integer
- Ruby: Implement Write Barriers
- See also UPB changes below, which may affect Ruby C-Extension.

UPB:
- Implements upb_Message_DeepClone

- Other:
- Fix: missing -DPROTOBUF_USE_DLLS in pkg-config
- Avoid using string(JOIN..., which requires cmake 3.12
- Bump Abseil submodule to 20230125.3
- Fix btree issue in map tests.
- Fix declared dependencies for pkg-config
- Fix build for newlib
- Update usage disclaimer on FieldOptions.ctype
- Add config option to print 64-bit integers in JSON as unquoted ints if they can be losslessly converted into a 64-bit float.
- Version protoc according to the compiler version number.
- Fix shared object ABI exports
- Ensure VarintParseSlowArm{32,64} are exported with PROTOBUF_EXPORT
- Update the min required CMake version to 3.10