magnifier.js: Port to classes and clean up (#13591)

Port all objects to classes
Remove use of Lang.bind()
Remove use of Mainloop module
Clean up some deprecated Clutter usage
Fix up some code styling

No functional changes

Author: JosephMcc

js/ui/gestures/actions.js

@@ -522,11 +522,11 @@ var ZoomAction = class extends BaseAction {
         }
 
         if (zoom_in) {
-            Magnifier.magInputHandler._zoom_in();
+            Magnifier.magInputHandler._zoomIn();
         }
         else
         {
-            Magnifier.magInputHandler._zoom_out();
+            Magnifier.magInputHandler._zoomOut();
         }
 
         this.last_time = time;