Add alternate authentication mechanism if Face ID fails.

If “biometric app lock” is enabled and Face ID fails, there is no way to open Slide.

On the current iOS beta, when you’re wearing a mask and have an Apple Watch, the device will unlock via the watch. It would be nice if this feature could be added to slide (not sure if thats possible).

As a worst case backup, maybe another option would be to prompt for a pin used by Slide which is created in advance.