Add/update plumbing for generateChallenge

Also added check in BiometricService for user preference (enable/disable
face auth for apps). If disabled, BiometricPrompt returns
ERROR_HW_UNAVAILABLE.

Bug: 111548037
Bug: 111461540

Test: BiometricPromptDemo works

Change-Id: I94ef7fca693af9d5501f87035efbde47a47a0642