Mirror task visibility on task org leash

- Depending on the navigation mode, the task is either visible or not
  when entering PIP, and if it is not visible, initially hide the leash
  so that SysUI can control it's visibilty to prevent a flash

Bug: 156941210
Test: Introduce artificial delay on sysui taskAppeared() and verify that
      we don't see the task when entering pip in gesture nav (and that
      it still works in 3 button)

Change-Id: I291afd209af118ac178f8a6421d7df25974315f0