Exit dream within keyguard-going-away transition

This ensures that the dream will exit immediately and not be visible
after unlocking the device, by bundling the dream exit transition with
the keyguard unlock transition.

Bug: 333829441
Test: unlocked by swiping open bouncer on dream and using fingerprint
unlock
Flag: ACONFIG android.service.dreams.dismiss_dream_on_keyguard_dismiss
DISABLED

Change-Id: Ie4587704bcc23794ba841077e34b9c4a1ee1c3e7