Fix stem to be propagated to output jar name in java_library

Currently, java_library.stem property is not correctly reflected in the
output jar name in java_library when the module specifies
java_resource_dirs property. This change fixes the unexpected behavior
so that setting the stem property behaves as expected.

Test: go test ./java && m
Bug: 285843207
Change-Id: I0941fcea83c92f4c42ae415aa6ad9125da5cf57b