Checks for APK sharedUserIds that cross partition group boundaries.

This check is used when merging target files to ensure that a merged
build does not contain any APKs that share UID across builds.

Bug: 171431774
Test: test_common
Test: Use merge_target_files.py to merge two partial builds,
      observe no failures for inputs without colliding APKs.
Test: Use merge_target_files.py to merge two partial builds,
      observe failure for inputs that have an APK that shares a
      UID across input partition groups.
Change-Id: I9dc57216882741ae46a99cfd7847f34702c75582