Ensure consistent APEX variation for java_sdk_library and java_sdk_library_import

Previously, a java_sdk_library with shared_library = true would create
a variation per APEX because it depends on an sdkLibraryXml module
which generates a file containing the APEX name. However, a shared
java_sdk_library_import would create a merged APEX variation. The
inconsistent variations caused failures in sdkDepsReplaceMutator.

This change ensures that both java_sdk_library and
java_sdk_library_import create an APEX specific variation when their
shared_library property is true.

Bug: 190499958
Test: m nothing
      - ran the above command after modifying the test to reproduce the
        problem and then after fixing to verify that it fixed the problem.
Change-Id: Iee81776a8569db3e871c40cbde14d248dfeb56e4