Add GIDAuthorizationUtil class.

[Alex-4-Git]

The class GIDAuthorizationUtil contains two utility methods. It helps us test these methods easily and reduce the GIDSIgnInTest complexity vastly.

In GIDSignInTest there are some tests using an OIDAuthorizationRequest. In production GIDSignIn sends an OIDAuthorizationRequest to AppAuth to start the authorization flow. In GIDSignInTest we saved the request and use this to verify the parameters and scopes before sending it to an AppAuth mock. By extracting these method we can verify the request and scopes directly instead of verifying them along with the whole sign-in flow.