Stop face auth when we transition to unsupported posture, no-op otherwise on posture change.

Fixes: 262492399
Test: atest KeyguardUpdateMonitorTest
Test: manually,
  1. enroll face auth
  2. Go to an face auth unsupported posture for the device
  3. Go to a face auth supported posture for the device
  4. Check the logs to make sure face auth wasn't triggered momentarily.
Change-Id: Ic96ddde93d1f45c1bf667d6b32193e754a79bf06
Merged-In: Ic96ddde93d1f45c1bf667d6b32193e754a79bf06