Improve BiometricPrompt support for face + UDFPS

On devices with an available face and UDFPS sensor, show a
BiometricPrompt that first attempts to authenticate with face, falling
back to UDFPS if unsuccessful. This change is UI-only for now, and
follow-up work will be needed to coordinate fallback behavior between
sensors, rather than running both simultaneously.

Test: atest com.android.systemui.biometrics
Test: Manually tested BiometricPrompt on device

Bug: 172376593
Bug: 183220060
Change-Id: Ia128e97d2d831d14420ec015f32eaa589b8c38cd