Move from face-specific settings to generic biometric settings

Fixes: 184965821
Test: On various devices:
      adb shell settings put secure biometric_app_enabled 0/1
      adb shell settings put secure biometric_keyguard_enabled 0/1

Test: On face-only devices that shipped before S:
      Existing settings (settings > security > face unlock) are not
      affected and still work.

      Newly added secure settings do not take effect (as expected)

Test: atest com.android.server.biometrics
Test: atest KeyguardUpdateMonitorTest

Change-Id: Ie0fda46facefd3ecfbbce6ef769d6d8e9fdfb09b