Apex: Add general presubmit tests

Just refer to subdirectories with runnable tests. This ensures
apexer changes lead to apex_file_test runs etc.

Test: atest --test-mapping system/apex
Change-Id: Icf2d3fa037dfb71cbe67362dc888a88e790530fa
1 file changed
tree: 1d02879ea1fce5ddfb4a661573cef4ad5194f551
  1. apexd/
  2. apexer/
  3. proto/
  4. tests/
  5. OWNERS
  6. PREUPLOAD.cfg
  7. TEST_MAPPING