Integration of precompiler jar files in extension

Not sure if documented way works now ( though we didn't break in intentionally ).
Known working ways are either
1 ) setting extension type to 'brebuilt' ( see openssl.so extension for reference. It only contains native .so libs but you should be able to put jars as well ( put them inside ./ext/platform/android ).
or
2 ) implement prebuilt part of your extension as .aar dependency and include it to your extension's build.yml in the 'maven_deps' section. The aar should be available at one of the repositories searched by the build system, look here:
github.com/rhomobile/rhodes/blob/master/platform/android/build/maven_deps_extractor.rb#L35

We can also provide more convenient solution that suits your needs.