Log Message:
{py-,}protobuf: update to 3.19.0

  C++
  * Make proto2::Message::DiscardUnknownFields() non-virtual
  * Separate RepeatedPtrField into its own header file
  * For default floating point values of 0, consider all bits significant
  * cmake: support `MSVC_RUNTIME_LIBRARY` property (#8851)
  * Fix shadowing warnings (#8926)
  * Fix for issue #8484, constant initialization doesn't compile in msvc \ 
clang-cl environment (#8993)
  * Fix build on AIX and SunOS (#8373) (#9065)
  * Add Android stlport and default toolchains to BUILD. (#8290)

  Python
  * Proto2 DecodeError now includes message name in error message
  * Make MessageToDict convert map keys to strings (#8122)
  * Add python-requires in setup.py (#8989)
  * Add python 3.10 (#9034)