SystemUI: Fix bad QS scrim colors due to race in brightness mirror state

[iusmac]

• When adjusting the brightness and "qs_ui_refactor_compose_fragment"
  flag is enabled, the NotificationPanelViewController (NPVC) will act
  as BrightnessMirrorShowingInteractor, which will directly animate the
  QS panel alpha when showing/hiding the brightness slider mirror.

  Currently, NPVC races with the legacy ScrimController, which manages
  the entire QS scrim lifecycle, including animating the scrim alpha
  during QS transitions (see logs below). As a result, it causes visual
  inconsistencies, such as the scrim color flashing or locking to a
  Color.BLACK when brightness mirror is gone.

  This patch adds a flag to track specifically the transitioning to/from
  BRIGHTNESS_MIRROR, preventing the ScrimController from altering scrim
  colors/alpha properties that may be already handled by NPVC.

Fixes crdroidandroid/issue_tracker#956
Fixes crdroidandroid/issue_tracker#1052

---

[START DRAGGING THE BRIGHTNESS SLIDER]
QS panel will disappear when showing the brightness mirror.

  D  ScrimController internalTransitionTo to state BRIGHTNESS_MIRROR
  D  ScrimController State changed to: BRIGHTNESS_MIRROR
  D  ScrimController Applying state: BRIGHTNESS_MIRROR
  D  ScrimController updating scrim behind_scrim color: 0
  D  ScrimController updating scrim behind_scrim alpha: 0.0
  D  ScrimController updating scrim notifications_scrim color: 0     <-- QS panel is now of Color.BLACK
  D  ScrimController updating scrim notifications_scrim alpha: 0.0   <-- QS panel became invisible
  D  ScrimController updating scrim front_scrim color: 0
  D  ScrimController updating scrim front_scrim alpha: 0.0
  D  ScrimController onFinished : state=BRIGHTNESS_MIRROR
  D  NotificationPanelView com.android.systemui:id/notification_panel: onBrightnessMirrorShowingChanged(isShowing=true)
  D  NotificationPanelView com.android.systemui:id/notification_panel: setAlpha(alpha=0, animate=true)

[STOP DRAGGING THE BRIGHTNESS SLIDER]
QS panel will reappear after hiding the brightness slider but the scrim color remains black.

  D  ScrimController internalTransitionTo to state KEYGUARD
  D  ScrimController State changed to: KEYGUARD
  D  ScrimController Applying state: KEYGUARD
  D  ScrimController updating scrim behind_scrim color: 0
  D  ScrimController updating scrim behind_scrim alpha: 1.0
  D  ScrimController updating scrim notifications_scrim color: 0     <-- QS panel is still of Color.BLACK
  D  ScrimController updating scrim notifications_scrim alpha: 1.0   <-- QS panel visible again
  D  ScrimController updating scrim front_scrim color: 0
  D  ScrimController updating scrim front_scrim alpha: 0.0
  D  NotificationPanelView com.android.systemui:id/notification_panel: onBrightnessMirrorShowingChanged(isShowing=false)
  D  NotificationPanelView com.android.systemui:id/notification_panel: setAlpha(alpha=255, animate=true)
  D  ScrimController onFinished : state=KEYGUARD