On fold/unfold, recalculate notif count immediately

One of the dependent flows was using shareIn, which prevents
the combine from running right away. Switching to stateIn
allows caching of the last value, which is the correct model
for this. Fold/unfold triggers this because the view is
detached then reattached, causing the previous coroutine
to stop and a new one to start.

Fixes: 331164146
Test: atest SharedNotificationContainerViewModelTest
Flag: ACONFIG com.android.systemui.migrate_clocks_to_blueprint
TEAMFOOD

Change-Id: Ib5ce8e77f6e07c925398a3ccc4af9144894cad43