Use alternateBouncerShowing instead of mOccludingAppRequestingFace to trigger...

Use alternateBouncerShowing instead of mOccludingAppRequestingFace to trigger face auth while secure camera is launched.

 - mOccludingAppRequestingFace is set to true by `UdfpsKeyguardViewController#showUdfpsBouncer`
 - This doesn't happen for devices with non-UDFPS fingerpint sensors.
 - Using alternateBouncerShowing would work better here.

Other changes:
 - Renames udfpsBouncerShowing to alternateBouncerShowing

Fixes: 267132953
Test: atest KeyguardUpdateMonitorTest
Test: manually,
  1. Enroll fingerprint (non-udfps) & face
  2. Suspend phone and go to Aod/Lockscreen
  3. Double press power button to open camera over lockscreen
  4. Open the gallery from the camera app.
  5. Alternate FPS bouncer should be shown and face auth should also run
Change-Id: I05d4256169a6fe491ed3c3be1cd6690341ad931f