Optional ReadonlyaskAsk the user which provider a reply should use when the person it is for last wrote through
another one. Resolve undefined on dismiss, which stops the send with denied:cancelled.
Without it the message leaves through the provider the order picked.
Optional ReadonlyonCalled with a frozen snapshot after every change to the preferences.
Optional ReadonlypreferencesPreferences saved by an earlier session. Providers named here are enabled as they are registered.
Options for createMessagingRegistry.