Finds APK shared UID violations when merging target files.

This involved moving the find-shareduid-violation.py script to
releasetools to simplify the cross-tool usage. This new location aligns
this script with other similar python host tools.

In a future change this violation file will be used to check for
shared UID violations across the input build partition boundary.

Bug: 171431774
Test: test_merge_target_files
Test: Use merge_target_files.py to merge two partial builds,
      observe shared UID violations file contents in the result.
Test: m dist out/dist/shareduid_violation_modules.json
      (Checking that existing behavior in core/tasks is presereved)
Change-Id: I7deecbe019379c71bfdbedce56edac55e7b27b41