Gesture recognizers unnecessarily produce registrar methods calling into generic class

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

https://github.com/xamarin/xamarin-macios/blob/403d01749f5920690ef87603b7bb0cb94ce3e868/src/UIKit/UIGestureRecognizer.cs#L79-L92

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