Update default size limit of CodedBufferReader from 67,108,864 bytes to 2,147,483,647 bytes, and default recursion limit from 64 to 100.

The new limits are consistent with the Java and C++ implementations. (#1060)

Fix GeneratedMessage.addExtension returning non-frozen and GeneratedMessage.getExtension allowing modifying an extension when the message is frozen before initializing the extension field set. (#1062)

Fix GeneratedMessage.getExtension returning differently typed lists when the message extension field set is initialized and frozen and initialized but not frozen. (#1062)

Fix PbList methods addAll, insertAll, replaceRange, setAll, setRange iterating the Iterable argument twice. (#730, #1070)

Fix GeneratedMessage.== throwing a type error when comparing map fields in some cases. (#1075, #1077)

This bug was introduced with protobuf-5.0.0.