[local_auth_darwin] Handle when FaceID hardware is available but permissions have been denied for the app

[jmagman]

LocalAuth -canEvaluatePolicy:: returns error LAErrorBiometryNotAvailable when either Face ID isn't available at the hardware level, OR the Face ID is available/setup but the permissions for the app were denied.

If it returns LAErrorBiometryNotAvailable, also check biometryType since this should be none if there really is no biometry, but gets populated with LABiometryTypeTouchID when the FaceID hardware is available, but permission is denied. I tried this on a iPhone 16 Pro which has Face ID but not Touch ID support.

Fixes flutter/flutter#160083

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