Don't detach recents from app window after motion pause

- Update MotionPauseListener to have 2 methods: the existing
  onMotionPauseChanged(isPaused) and onMotionPauseDetected()
  - onMotionPauseDetected is the default as most listeners only
    care about the first detected pause
  - AbsSwipeUpHandler still listens to pause changes, to help
    determine the end target at the end of the gesture

Bug: 159089437
Change-Id: I6d14f106cdcbe4e07d8dddba1cee909a963615b1