Enable FASS assertions for IME Appear

Add a new test rule to OpenImeWindowTest for comparing the new FASS
assertions with the old flicker testing. If the flicker tests from one category
(presubmit/postsumbit/flaky) are passing or failing, the corresponding
FASS test should have the same behaviour.

Bug: 201523242
Test: see the results in the dashboard go/wm-tests-flicker
Change-Id: I018c657f12cfbf2377b4353c13981f2c000f6ccf