_java_bin

See if we can replace [_java_bin](https://github.com/bazelbuild/rules_scala/blob/c81d7cd52d9648cbbc998e3ddc6d9e975890e6b2/scala/private/rule_impls.bzl#L596) with code from rule_java or something (existing or to contribute back).
Motivation for generalization- Recurring pattern of finding the java bin folder