Credential FRP: Add implementation

- Adds a facility to store a credential handle that survives factory reset
- Adds a method to KeyguardManager for verifying the stored credential for SetupWizard
- Dark launches persisting the primary user's credential as the FRP credential (behind a default-off flag)

Future work:
- Use a separate GK handle / synthetic password for the FRP credential
- Enroll the FRP credential in verifyCredential for the upgrade case

Bug: 36814845
Test: runtest -x core/tests/coretests/src/com/android/internal/widget/LockPatternUtilsTest.java && runtest -x services/tests/servicestests/src/com/android/server/LockSettingsStorageTests.java && runtest -x services/tests/servicestests/src/com/android/server/SyntheticPasswordTests.java
Change-Id: Ia739408c5ecb169e5f09670cd9ceaa7febc2b1cc