(Fix-forward) Emit notificationsAlpha=0f earlier in the OCCLUDED->LS transition.

This workaround is required until we tie shade expansion to keyguard transitions (tracking in b/332946323).

Fixes: 332877794
Test: atest SystemUITests
Test: launch camera w/ notifs and then go back
Flag: ACONFIG com.android.systemui.migrate_clocks_to_blueprint TEAMFOOD
Change-Id: Iba9b5a8f5698e8739f8cfcf742cc9b50b7fee542