convert java_plugin with bp2build

Also, because java_plugin is only intended to be built for the host
platform to make additions to the javac compiler, a compatibility
requirement is added to java_plugin that ensure that it is not built
for android targets.

Bug: 215229742
Test: go test ./bp2build
Change-Id: I09902215a9f1e8b14d4de5a51328d08a7a0a4450