Preload overview activity in background

To reduce the jank when swiping-up the overview which is not
ready yet, we restart the overview activity if the process
was died and update its configuration if there is change.

Bug: 127350205
Test: manual - Enable 2-button or gesture navigation.
      Swipe-up overview after:
      Case 1: Other app is in foreground and kill the process
              of launcher.
      Case 2: Change configuration, e.g. font size, language.

Change-Id: Ia6e365cc0faf3765781484d040bdddd4e10a2650