[firebase_ui_auth] Remember last known login method on a device

[aebrahim]

One of the downsides of supporting multiple social logins is that end users often forget which method they used to log in. This is especially true on apps which enforce automatic sign out. However, on re-login, it would be extremely convenient to highlight the last used method for social login. This information would be relatively simple to store in local storage.

Here is a visual mock-up of what this might look like:

As far as implementation goes, I believe this would require only a few things:

1. A configuration option to toggle this behavior
2. Storing the last used login method on device.
3. A new translated string to use in the case of "Last sign in"

Is there any interest in a feature like this? We were planning on building it ourselves, but we would rather collaborate on an open-source solution, and this seems like a general problem that I'm sure other folks are dealing with as well.