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: I3c71927f26a218e8b2b7e3ceea99cf8ba79d828f