Since this is the rake target used by kokoro, this will close the gem release gap for JRuby

Should help protocolbuffers#7923 by making sure JRuby is built and released as part of the normal cadence.

…olves most test failures under JRuby 9.2.11.1

…olves most test failures under JRuby 9.2.11.1

…tests

# Conflicts:
#	ruby/src/main/java/com/google/protobuf/jruby/RubyDescriptorPool.java

…olves all unit test failures under JRuby 9.2.11.1

…tests

…#8999)

…uffers#8945)

* Protobuf: Fix for C5041 for VC++ > 15.5

Introduced in 15.5: https://docs.microsoft.com/en-us/cpp/overview/cpp-conformance-improvements-2017?view=msvc-160#inline-variables
15.5 is 1912: https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros?view=msvc-160

Issue: protocolbuffers#8978

* Fix comment wording for protocolbuffers#8978

* deps: add j2objc annotations

@pzd this will be needed on the next sync with google3

…xed, and signed scalar types as supported map keys.

Reset JRuby conformance test expectations to align with the superset of expected failures from both Ruby and Java.

Includes minor cleanups to fix typos, to remove unused variables, unused private methods, and unused imports, and improve formatting.