Support nesting in leaftaskfilter and make recents compatible

The filter only checked "every-other" level because it would
return early if it found a child; however, split-screen is
>1 layer deep, so we actually need to still record the task
as a child so its parents will also be rejected.

This exposed an issue in RecentsHandler where it wouldn't
reset the task surface visibility of root tasks when
cancelling (going-back to app), so this fixes that as well
by tracking leafs and roots but only forwarding the leafs to
launcher

Bug: 283176051
Test: put windows in split, swipe into overview, observe transition
      info in logs.
Change-Id: Ib545792891bad93104892a55ad7059eff7b7a623