Fix issue with inconsistent stage visibility

- Prior to ag/29842477, the stage coordinator visibility was inaccurately
  tracked (ie. when PIP is expanded over a split pair, the visibility
  state remained true), which resulted in the divider visibility being
  wrong as well and inadvertently, the visible state resulted in split
  participating in some transition flows like
  DefaultMixedTransition.createRecentsMixedTransition() which did end
  up correctly updating the split state following the next swipe up.

  However, after the above change, split was no longer participating in
  those flows, but nothing was also changed to run the logic following
  the stage visibilty changes, which normally calls
  setReparentLeafTaskIfRelaunch() to ensure that hidden split tasks can
  be launched into fullscreen if either task in the pair is relaunched.

  This CL instead tweaks ag/29842477 to update the listener visibility
  whenever the root task info changes, to ensure that we don't
  inadvertently report visiblity changes when going from split pair ->
  split pair (which can generate multiple leaf child task visibility
  changes.  This also allows us to mostly revert ag/30237116 since that
  inconsistency is resolved.

Fixes: 380016062
Flag: EXEMPT bugfix
Test: go/split-smoke-test
Test: Verified that both b/289753648 and b/358065655 remain fixed
Change-Id: Ie4d8513838308f5330588fc3fe905f0661bbeab3