Hide overview actions when desktop is focused

Use same logic for desktop as split screen is using. If focused task is
the desktop task, hide overview actions.

Bug: 269658609
Test: Enable desktop proto 2, have some apps on desktop, focus on a
  fullscreen app, open overview, observe actions visible
Test: have some apps on desktop, open desktop, open overview, observe
  actions are not visible
Test: open two apps in split screen, go to overview, observe no actions
  visible
Change-Id: I7de28ea7af93b58379bb539c5a1b1bcbf6d13b83