Prioritize keyguard going-away over occlude transition

If the occluding/unoccluding activity is dismissing the keyguard,
we want to play the dismissing-keyguard animation and then reset
mKeyguardGoingAway, rather than just playing an occlusion animation
and leaving mKeyguardGoingAway permanently set.

Bug: 355617360
Test: atest CtsWindowManagerDeviceKeyguard
Flag: EXEMPT bugfix
Change-Id: Ib11609c5ca82c5318a94faa3bf3fdc1f7bbe7192