Keyguard: Improve trusted unlock while occluded

Smoothly unlocks device when going from a SHOW_WHEN_LOCKED activity
to a DISMISS_KEYGUARD activity while the device is trusted.

This change suppresses the jank from going briefly through the
lockscreen if the device is trusted and unlockable without entering
a credential.

Bug: 27410215
Change-Id: Idd86e825d37a89538a0a1f690daf6afcf94a0699