Update screen decor overlays when face auth sensor changes

The face auth sensor location may not be available when
ScreenDecorations initially adds the overlay. If the location
is available later, then the face scanning overlay should be
added.

Test: Reboot device and observe face scanning animation can
be seen when face auth runs (without requiring config change).
Flag: NONE
Test: atest ScreenDecorationsTest
Fixes: 333088555

Change-Id: Id27ddece6b8ebc71ef7ba0e035cff869d91f7b56