Protobuf

C++
* Reduce memory consumption of MessageSet parsing
* This release addresses a [Security Advisory for C++ and Python users](https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-8gq9-2x98-w8hf)

PHP
* Added getContainingOneof and getRealContainingOneof to descriptor.
* fix PHP readonly legacy files for nested messages

Python
* Fixed comparison of maps in Python.

C++
* Reduce the required alignment of ArenaString from 8 to 4 (10298)

C++
* Add header search paths to Protobuf-C++.podspec (10024)
* Fixed Visual Studio constinit errors (10232)
* Fix 9947: make the ABI compatible between debug and non-debug builds (10271)

UPB
* Allow empty package names (fixes behavior regression in 4.21.0)
* Fix a SEGV bug when comparing a non-materialized sub-message (10208)
* Fix several bugs in descriptor mapping containers (eg. descriptor.services_by_name)
* for x in mapping now yields keys rather than values, to match Python conventions and the behavior of the old library.
* Lookup operations now correctly reject unhashable types as map keys.
* We implement repr() to use the same format as dict.
* Fix maps to use the ScalarMapContainer class when appropriate
* Fix bug when parsing an unknown value in a proto2 enum extension (protocolbuffers/upb717)

PHP
* Add "readonly" as a keyword for PHP and add previous classnames to descriptor pool (10041)

Python
* Make //:protobuf_python and //:well_known_types_py_pb2 public (10118)

Bazel
* Add back a filegroup for :well_known_protos (10061)

C++
* ArenaString improvements (fix alignment issue)

PHP
* API changes for OneOf (10102)

C++
* cmake: Revert "Fix cmake install targets (9822)" (10060)
* Remove Abseil dependency from CMake build (10056)

Python
* Update python wheel metadata with more information incl. required python version (10058)
* Fix segmentation fault when instantiating field via repeated field assignment (10066)