Retry: "java_sdk_library: Access outputs using tags"

Previously, in order to access say the public stubs source jar it was
necessary to directly reference the module by name. This change adds
support for accessing them indirectly via tags.

Test: nothing
Bug: 155164730
(cherry picked from commit 46dc45ab)
Change-Id: Icc21caee5b4b1da6f958470bd7bae8a37933f24b