base

Fix layering and launching issues.

- Replace calls to ActivityStack.resumeTopActivity() with calls to
ActivityStackSupervisor.resumeTopActivities().

- Move dim layers from display scope to stack scope. This applies to
both the animation background dim layer and the FLAG_DIM_BEHIND dim
layer.

- Move windows on stacks that are not targeting wallpaper above the
wallpaper. Otherwise wallpaper placement hides the non-focused stacks.

Change-Id: Ic6b97ac6b094672bb1ddac17ce46ea58c738f073