[flexiglass] Don't clear pending keyguard dismiss action when...

...when transitioning from alternate bouncer to primary bouncer.

There are several parts to this work:
1. Eliminate the logic that was clearing the dismiss action based on a
   flow of events
2. Clear the dismiss action explicitly when hiding the alternate bouncer
   from everywhere except when knowingly transfering to the primary
   bouncer
3. Clear the dismiss action explicitly when leaving the primary bouncer

Fix: 379848880
Test: manually verified the verification scenarios in comment#7 of the
attached bug
Test: unit test coverage added
Flag: com.android.systemui.scene_container

Change-Id: Ib3800d5956dd074aaa06e91662f23e81c759036c