Support automatic registration of covariant implemented interfaces

[kzu]

If a type implements a covariant interface, automatically register the
compatible covariant types for it.

For example, given:

public interface IEvent { }
public class BaseEvent : IEvent { }
public class MyEvent : BaseEvent { }
[Service]
public class ObservableService : IObservable<MyEvent>
{
}

Registrations should include: IObservable<MyEvent>, IObservable<BaseEvent> and
IObservable<IEvent>, since all of them can be used in a covariant way with the
same service implementation.