make recognizer public

Runtime/gestures/scale.cs

     }
 
 
-    class ScaleGestureRecognizer : OneSequenceGestureRecognizer {
+    public class ScaleGestureRecognizer : OneSequenceGestureRecognizer {
         public ScaleGestureRecognizer(object debugOwner) : base(debugOwner: debugOwner) {
         }