Define additional error codes in VerifyCredentialResponse

Define some new response codes in VerifyCredentialResponse so that more
detailed error information can be reported to SystemUI and to
LockSettingsService itself:

    RESPONSE_CRED_TOO_SHORT
    RESPONSE_CRED_ALREADY_TRIED
    RESPONSE_CRED_INCORRECT

This CL simply adds and documents the enum values, without using them.
Later CLs will start using these new codes.

Test: atest FrameworksServicesTests:com.android.server.locksettings
Bug: 395976735
Flag: EXEMPT just adding new enum values that aren't used yet
Change-Id: If6878b6a229804cd86b9e6364345937ca7a6d533