Polish a weird transition that open animation can apply on non-top task.

When app relaunch an translucent activity then clear any activities
above it, if above activity(ies) was opaque and fill_task, that
startActivity transition will also collect any below activity/task due
to it become visible.
But that visible change can confuse DefaultTransitionHandler because it
will create an opening(slide-in) animation for the non-top change.
Add the OCCLUDED flag for those changes which belows non-translucent
target, so they can be filter out if no animation is requested.

Bug: 318877215
Test: repeatly launch OmnientActivity while CCT is above it, verify
no strange opening task animation occur.

Change-Id: Idce88c839b26db1def7aec0a220bfb8110c54e5c