Roscoe

Results 2 issues of Roscoe

**What this PR contains** Added support for mocking getIdTokenResult. Most useful for custom claims, which can be used for role-based access control. - Adds ```IdTokenResult? _idTokenResult``` private property in MockUser...

Most useful for custom claims, which can be used for role-based access control. ``` dart /// Returns a [IdTokenResult] containing the users JSON Web Token (JWT) and /// other metadata....