WM: Cleanup TestAppWindowToken code and promote ZOrderingTests to non-flaky

- Followup from commit:aab3d3d7 to not skip onParentChanged when creating TestAppWindowToken.
- This is not needed since we are mocking SurfaceControl and Transaction native calls by
  default.

Fixes: 127948929
Test: atest WmTests
Change-Id: I7cfc464016d9d77fcf4ac418417668d38b897157