Integrate recent animation of single-root split with shell transition

Stop propergating child task information up if the parent task having
multiple child task changes in the same transition. And skip wrapping it
into the final remote animation targets so its child tasks won't get
transfered multiple-times in such transition.

Bug: 207185041
Bug: 206487881
Test: enabled shell-transition and triggered split screen, observed
      the recent animation works properly
Change-Id: I8d2c62df99ccb88303aa2b06dd18f2f4edb330f2