Force behind and notification scrim alpha to be 0 when the device is unlocking.

For dreaming -> unlocked transition:
 - mExpansionAffectsAlpha is false while ScrimController applyState is invoked, it early returns with the behind and notif alphas set to 0.45ish from UNLOCKED scrim state
 - This CL handles this scenario

For keyguard -> unlocked transition:
 - mExpansionAffectsAlpha is false initially and ScrimController starts applying UNLOCKED state alphas (0.45ish)
 - CentralSurfaces#updateScrimController gets invoked, keyguard showing is now false and it sets mExpansionAffectsAlpha to true
 - ScrimController#onUnlockAnimationFinished is then invoked which invokes applyAndDispatchState which re-applies UNLOCKED scrim state
 - mExpansionAffectsAlpha is now true, early return doesn't happen in applyState
 - behindScrimAlpha and notifScrimAlpha get reset to 0 later in the applyState method.

Fixes: 406364098
Test: verified manually,
  1. setup fingerprint on a power button FP device
  2. Enable screensaver
  3. Go to screensaver
  4. Touch the power button to authenticate while on the screensaver
  5. Device unlocks and goes to launcher without leaving the behind scrim on the screen.

Flag: com.android.systemui.notification_shade_blur
Change-Id: I6898a47069550bc5305dc8b8650f132668fcd998