Add `-[GIDSignIn signInWithCompletion:]` to provide sign in mechanism without a `presentingViewController`

[mdmathias]

GIDSignInInternalOptions, depending upon whether or not we are on macOS or iOS, will need to be created with a nil presentingWindow or presentingViewController.

The sign in with hint methods will also need to be updated similarly as well.

-[GIDSignIn signInWithHint:completion:]
-[GIDSignIn signInWithHint:addAdditionalScopes:completion:]

Last, the -authenticateInteractivelyWithOptions: method needs to be updated to handle the nil window or view controller case. The new implementation will make use of the new +[OIDAuthorizationService presentAuthorizationRequest:callback:] method outlined in the related milestone on AppAuth-iOS.

[amit2908]

@mdmathias I am facing an issue in which after SFSafariViewController dismissal, my view controller doesn't animate back to its original form, resulting in a damaged view after google sign in.

[mdmathias]

Hi @amit2908; sorry to hear you're having a problem. This issue tracks progress on a project we're thinking about internally, and probably isn't the right place to discuss your question.

If you would like to file an issue on this repository, then please choose from one of our templates. Otherwise, if this is a general request for help, please refer to our documentation, look at our examples, or feel free to ask a question on stackoverflow.

I will leave this here for a little bit so that you can see my message, but will be deleting this and your post to keep the issue's comment history relevant to its subject for future reference.