[PB] Do not cancel animation from transition.

Since we are migrate PB to shell transition, core does not need to
cancel animation while received another transition, just let the
transition happen, and let shell side to handle it.

Keep track animated target after PB animation finish by detect app
visibility change. When canceled and previous animation was start
with launch behind, start a CLOSE_PREPARE_TRANSITION to collect
changes, as the last step of cancel transition.

In BackTransitionHandler, ignore transition if the content of changes
are not expected, so DefaultTransitionHandler will handle it.

Flag: com.android.window.flags.migrate_predictive_back_transition
Bug: 340386663
Test: trigger close or open transition with a button where close to the
edge of device, so when click on the button, PB and another transition
will be triggered almost at the same time. Verify BackTransitionHandler
can skip PB by changes if possible.

Change-Id: I65ca37905a883a17d1a39dd609fd9e9c91bf8988