* Make message-type extensions merge from wire-format instead of building up instances and merging afterwards. This has much better performance.
* Fix TextFormat parser to build up recurring (but supposedly not repeated) sub-messages directly from text rather than building a new sub-message and merging the fully formed message into the existing field.
* Fix bug in nested builder caching logic where cleared sub-field builders would remain dirty after a clear and build in a parent layer. https://github.com/protocolbuffers/protobuf/issues/10624
* Performance test for TextFormat to verify fix for https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-h4h5-3hr4-j3g2
Python
* Changes ordering of printed fields in .pyi files from lexicographic to the same ordering found in the proto descriptor.