Gesture recognizers unnecessarily produce registrar methods calling into generic class

[filipnavara]

Static registrar calls are extremely inefficient when the target is a generic class. This happens to produce that code in the binding themselves:

xamarin-macios/src/UIKit/UIGestureRecognizer.cs

Lines 79 to 92 in 403d017

	[Register ("__UIGestureRecognizerGenericCB")]
	internal class Callback<T> : Token where T : UIGestureRecognizer {
	Action<T> action;
	internal Callback (Action<T> action)
	{
	this.action = action;
	}
	[Export ("target:")]
	[Preserve (Conditional = true)]
	public void Activated (T sender) => action (sender);
	}

It can likely be avoided by introducing non-generic parent. It's also a non-issue with the new managed static registrar.