Add smart magnify gesture support for macOS (#2554)

* Add smart magnification gesture

* Deliver position of smart magnification event

* Document smart magnification event

* Revert "Deliver position of smart magnification event"

This reverts commit ac0e61a9a4.

* Remove mention of touchpad from smart magnification event

* Update change log

* Mention minimum macOS version supporting smart magnification

* Improve doc

src/platform_impl/macos/view.rs

@@ -858,6 +858,20 @@ declare_class!(
             AppState::queue_event(EventWrapper::StaticEvent(window_event));
         }
 
+        #[sel(smartMagnifyWithEvent:)]
+        fn smart_magnify_with_event(&self, _event: &NSEvent) {
+            trace_scope!("smartMagnifyWithEvent:");
+
+            let window_event = Event::WindowEvent {
+                window_id: self.window_id(),
+                event: WindowEvent::SmartMagnify {
+                    device_id: DEVICE_ID,
+                },
+            };
+
+            AppState::queue_event(EventWrapper::StaticEvent(window_event));
+        }
+
         #[sel(rotateWithEvent:)]
         fn rotate_with_event(&self, event: &NSEvent) {
             trace_scope!("rotateWithEvent:");