Respect hierarchy visibility of transient launch

This fixes two cases:
1. When swiping to home with pip or freeform on top, the transient
   launch (home or recent) is misjudged as occluded because the
   always-on-top task is also opaque.
2. After swiping to another app, even if recent is occluded by
   the new top, the recent is still considered as visible before
   the transition is finished.

Bug: 362033992
Flag: EXEMPT bugfix
Test: TransitionTests#testIsTransientVisible
Change-Id: I52bb8ecbed7437107c776ad5fdd4b4d4d4d4f962