[flexiglass] Clean up Gone -> Shade -> QS transitions

Various cleanups:
- Cleans up NotificationScrim transition into QS scene
- Ensures Shade and QS background scrim are rendered behind other elements during scene transitions
- Disabled SharedNotificationContainerBinder controlling NSSL alpha when flexi-notifs is enabled (fixes flickering)
- Animated corner radius during Gone -> Shade transition
- Device corner radius is provided via CompositionLocal, notifs scrim corner radius source of truth moved out of StackAppearanceRepository
- Fixes Shade -> Gone transition when notif scrim is expanded

Bug: 296118689
Test: manual
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Change-Id: I8461125ab6e76c15cccdab1d92df41a5dacbd442