Add some overview of the java module types so that we have something
to display in the autogenerated docs.
Bug: 67909957
Test: m soong_docs
Change-Id: I3594dd550f8272f4418f3ea12cded4083674809b
Add a java_genrule that has the right multilib flags to be a
dependency of a java rule. Make java libraries implement
SourceFileProducer so that their classes jar can be used as an
input to a java_genrule. Allow libs and static_libs dependencies
to be a java_genrule.
Test: TestJarGenrules
Change-Id: Ib1b31ef9c0b7e72eeed2c9ecc4ce8a1088e0b1c9