Improve data separation test coverage

Two areas need better coverage:
1. Tests are not verifying that files in /data/vendor do not have the
core_data_file_type attribute.
2. No error is thrown if a type lives in both /data/vendor
/data/<not vendor>.

Bug: 72998741
Test: build all selinux policies on master (assert build time tests)
Test: build and boot Marlin and Taimen, verify no selinux denials and
    everything works as expected.

Change-Id: I133a068123139a599b9b81ddcc254616894621eb
(cherry picked from commit 55d5e284)