Merge closing transition when recents is running

If the incoming transition clears all pausing task, the handler
only needs to consume it because the task is either already
disappearing by swipe-up animation or is kept showing on recents.
Otherwise it may go DefaultTransitionHandler and apply a weird
animation depends on the change info.

Bug: 279142303
Test: When swipe-to-home animation is running, the current task
      finishes itself. There should be no additional animation.
Change-Id: Id671e0cc3ddb3736e1e33f14138dacbe05631c9c