Added animations to dim layers

Added animations to dim layers when dims are set for
WindowState surfaces since they're controlled by the system.

Test: Dims for dialogs now animate.
Test: DimmerTests
Fixes: 71841698
Fixes: 69553362
Fixes: 71614627
Fixes: 72333587

Change-Id: I34f6f3d7885d5c9c0075a941e40d68bc5618a016