FRP: Explicitly throw UnsupportedOperation when FRP is not supported

Changes KeyguardManager.createConfirmFactoryResetCredentialIntent such that
it throws UnsupportedOperationException when credential-based FRP is not
available on the device (either because storage was corrupted, or the device
simply does not support it).

This allows GMScore to distinguish this case from when the previous owner
simply didn't set up security.

Also fixes a few places where we previously unintentionally crashed with an
NPE.

Bug: 72368658
Test: atest LockSettingsStorageTests
Change-Id: I92fe1d4b06834e76a4bfffad41276ca28c68ce70