Make CommunalSurface fullscreen and at the correct z-order level.

This change updates the CommunalSurfaceView to be full screen,
relocating to be a direct child of the notification panel. It also
removes logic to make the view sit ontop of the z-order.

Test: manual
Bug: 197036940
Change-Id: I1ee59f1da26c2a180e66b61fa6e309e767d78cf2