Terminal.Gui: TextValidateField has XML doc errors

@BDisp Thanks!!. I will change it, send PR and then we see.

Other implementation will keep working, because the providers are the implementation. The only diff is that we passit via contructor, and it’s not created with the activator.

public class MyProvider : ITextValidateProvider{}

var field = new TextValidateField(new MyProvider{});

Any thoughts on this? should we change it to just handle each generic explicitly e.g.

View CreateClass (Type type)
{	
	View view;

	if(type == typeof(TreeView<>)) {
		view = new TreeView<object> ();
	} else {
		view = (View)Activator.CreateInstance (type);
	}

The problem is if it has a bunch of generic types later, it needs to changes for each of them.