Fix app widget deadlock when toggling overlays

AppWidgetManager uses ActivityManager so we must update it without
holding the AMS lock.

Bug: 195649929
Bug: 193866093
Test: Repeatedly change wallpaper & style color to a "basic" color
      and go back to launcher to observe overlay correct color is
      applied
Change-Id: I7a3ba2af026b98c87da8ebbe4dbca602f8c4bcf2