- add 10355.patch to fix soversioning

- update to 21.4:
* Reduce the required alignment of ArenaString from 8 to 4

- update to 21.3:
* 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/upb#717)
* 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)