Add touchpad magnify and rotate gestures support for macOS (#2157)

* Add touchpad magnify support for macOS

* Add touchpad rotate support for macOS

* Add macOS rotate and magnify gesture cancelled phases

* Correct docs for TouchpadRotate event

* Fix tracing macros

examples/touchpad_gestures.rs

@@ -0,0 +1,43 @@
+use simple_logger::SimpleLogger;
+use winit::{
+    event::{Event, WindowEvent},
+    event_loop::{ControlFlow, EventLoop},
+    window::WindowBuilder,
+};
+
+fn main() {
+    SimpleLogger::new().init().unwrap();
+    let event_loop = EventLoop::new();
+
+    let _window = WindowBuilder::new()
+        .with_title("Touchpad gestures")
+        .build(&event_loop)
+        .unwrap();
+
+    println!("Only supported on macOS at the moment.");
+
+    event_loop.run(move |event, _, control_flow| {
+        *control_flow = ControlFlow::Wait;
+
+        if let Event::WindowEvent { event, .. } = event {
+            match event {
+                WindowEvent::CloseRequested => *control_flow = ControlFlow::Exit,
+                WindowEvent::TouchpadMagnify { delta, .. } => {
+                    if delta > 0.0 {
+                        println!("Zoomed in {}", delta);
+                    } else {
+                        println!("Zoomed out {}", delta);
+                    }
+                }
+                WindowEvent::TouchpadRotate { delta, .. } => {
+                    if delta > 0.0 {
+                        println!("Rotated counterclockwise {}", delta);
+                    } else {
+                        println!("Rotated clockwise {}", delta);
+                    }
+                }
+                _ => (),
+            }
+        }
+    });
+}