Grain state feature does not support state of generic Grain base type

[koenbeuk]

Just got a chance to use this: #360

The grain state feature works fine when my grain is shaped as:

class MyGrain : Grain, IMyGrain { 
  readonly IPersistentState<ProfileState> state;
 
  public MyGrain([PersistentState("profile", "profileStore")] IPersistentState<ProfileState> state) { 
    _state = state;
  }
}

and

class MyGrain : Grain, IMyGrain {  
  public MyGrain([PersistentState("profile", "profileStore")] IPersistentState<ProfileState> state) { 
    State = state;
  }

  protected IPersistentState<ProfileState> State { get; }
}

But not when:

class MyGrain : Grain<ProfileState>, IMyGrain {  }

If I'm correct, the recommended practice from Orleans is to use the constructor approach however the generic base type approach is just convenient and while we wait for primary constructors to be implemented in C#, I think we should consider adding support for this.

[koenbeuk]

At first glance, it seems that this could be implemented here: https://github.com/OrleansContrib/OrleansDashboard/blob/4b9dd9ed86038a0a6b254cc2ce5c8dfb6edbeb2b/OrleansDashboard/Implementation/Helpers/GrainStateHelper.cs#LL67C1-L67C1

Happy to issue a PR if there is an agreement that this is valuable.