FirebaseAppCheck getToken Method for protecting non-Firebase API resources

[jrfarrant]

AppCheck looks like a fantastic solution for helping secure backend resources. I can see that there is a 'getToken' method in the javascript AppCheck API, but I can't find an equivalent in the Flutter AppCheck API. I'd like to include the AppCheck token as a header in my custom (non-Firebase) API requests. This would perhaps make sense as a new method FirebaseAppCheck.instance.getToken().

Many thanks to the team, awesome set of tools you're building! Apologies if I have missed something obvious.