Cancel merges in RecentsTransitionHandler if it's always on top

Merging the bubble open animation with the recents animation results
in a bad and unrecoverable state for bubbles so skip the merge.

Test: manual - 1) have a bubble and a normal activity open
               2) swipe up to go home and tap on the bubble quickly
               => observe the bubble opens normally
Bug: 273966970
Change-Id: I577663869897b8781b0d5e670097afdb5b8b8524