Request face auth when exiting dreams

When the user taps to dismiss their dream, request face unlock similar
to how we run face auth when transitioning from AOD. This ensures the
user can quickly unlock after dismissing their dream.

Bug: 404585041
Test: enabled flag and dismissed dream, verified face auth triggers
Flag: android.service.dreams.dreams_v2
Change-Id: I6319939d5183e8443c82379a21403a7baeaa12e6