Generalize back animation and transition sequence...

for both shell and legacy transition system.

The general sequence will be:
1. Create animation leash in core, pass to remote animation runner.
2. Remote animation finish, collect finish transaction before
transition happen. Apply finish transaction here if back event won't
trigger.
3. Check whether next transition is triggered from back gesture via
checking the open/close targets.

The 3rd step introduce another change, which to let the back transition
happen. Instead of consume next transition, we should try to find out
whether the participant was the animation target, because we cannot
assume what the opening target will do in resume stage. For example,
the opening activity could finish itself, or start another activity at
onResume, so in either case, the opening activity will become closing
activity. We can only ensure that activity will participant in next
transition.
So the more robust way should be, find out those targets which were
animated. For shell transition, and add a flag to the corresponding
change, then the transition handler can determine what to do based on
the targets. For legacy transition, ignore those targets when estimate
the transition type in AppTransitionController#getTransitCompatType.

Bug: 238474994
Bug: 131727607
Test: varify transition can be handled for some unexpected scenario:
  1. launch new activity when close app.
  2. launch singleInstance activity when close app.
Test: do back gesture on both shell/legacy transiton system, verify
no flicker happen whenever the back is triggered.

Change-Id: I9364be25c608f7b5797577d26b57bc7d6f2dde9c