Support OneOfBase<T0, T1, ...> on FluentAssertions.OneOf

[julealgon]

• Library: FluentAssertions.OneOf
• Version: 0.0.5

Just downloaded your library in hopes that it would improve my unit tests without having to create custom FluentAssertions validators for my response objects.

However, I'm relying on custom responses like this:

public abstract class MyResponse : OneOfBase<MyResponse.Success1, MyResponse.Error1, MyResponse.Error2>
{
    public sealed class Success1 : MyResponse {}
    ...
}

As you can probably tell, the extensions in this library do not trigger for my type, because I'm not using the OneOf<T> type, but its base OneOfBase<T>.

Could you please change the validation extensions to consider the base type instead, so that both raw OneOf as well as discriminated union custom classes can be used?