macOS: Avoid redundant initial resize event (#3913)

The `NSViewFrameDidChangeNotification` that we listen to is emitted when
`-[NSWindow setContentView]` is called, since that sets the frame of the
view as well.

So now we register the notification later, so that it's not triggered at
window creation.

This behaviour is well described in the documentation:
https://developer.apple.com/documentation/appkit/nsview/postsframechangednotifications?language=objc

src/platform_impl/apple/appkit/window_delegate.rs

@@ -15,15 +15,15 @@ use objc2_app_kit::{
     NSAppKitVersionNumber, NSAppKitVersionNumber10_12, NSAppearance, NSAppearanceCustomization,
     NSAppearanceNameAqua, NSApplication, NSApplicationPresentationOptions, NSBackingStoreType,
     NSColor, NSDraggingDestination, NSFilenamesPboardType, NSPasteboard,
-    NSRequestUserAttentionType, NSScreen, NSToolbar, NSView, NSWindowButton, NSWindowDelegate,
-    NSWindowFullScreenButton, NSWindowLevel, NSWindowOcclusionState, NSWindowOrderingMode,
-    NSWindowSharingType, NSWindowStyleMask, NSWindowTabbingMode, NSWindowTitleVisibility,
-    NSWindowToolbarStyle,
+    NSRequestUserAttentionType, NSScreen, NSToolbar, NSView, NSViewFrameDidChangeNotification,
+    NSWindowButton, NSWindowDelegate, NSWindowFullScreenButton, NSWindowLevel,
+    NSWindowOcclusionState, NSWindowOrderingMode, NSWindowSharingType, NSWindowStyleMask,
+    NSWindowTabbingMode, NSWindowTitleVisibility, NSWindowToolbarStyle,
 };
 use objc2_foundation::{
     ns_string, CGFloat, MainThreadMarker, NSArray, NSCopying, NSDictionary, NSEdgeInsets,
     NSKeyValueChangeKey, NSKeyValueChangeNewKey, NSKeyValueChangeOldKey,
-    NSKeyValueObservingOptions, NSObject, NSObjectNSDelayedPerforming,
+    NSKeyValueObservingOptions, NSNotificationCenter, NSObject, NSObjectNSDelayedPerforming,
     NSObjectNSKeyValueObserverRegistration, NSObjectProtocol, NSPoint, NSRect, NSSize, NSString,
 };
 use tracing::{trace, warn};
@@ -170,7 +170,7 @@ declare_class!(
         #[method(windowDidResize:)]
         fn window_did_resize(&self, _: Option<&AnyObject>) {
             trace_scope!("windowDidResize:");
-            // NOTE: WindowEvent::SurfaceResized is reported in frameDidChange.
+            // NOTE: WindowEvent::SurfaceResized is reported using NSViewFrameDidChangeNotification.
             self.emit_move_event();
         }
 
@@ -658,9 +658,9 @@ fn new_window(
 
         let view = WinitView::new(
             app_state,
-            &window,
             attrs.platform_specific.accepts_first_mouse,
             attrs.platform_specific.option_as_alt,
+            mtm,
         );
 
         // The default value of `setWantsBestResolutionOpenGLSurface:` was `false` until
@@ -682,6 +682,23 @@ fn new_window(
         window.setContentView(Some(&view));
         window.setInitialFirstResponder(Some(&view));
 
+        // Configure the view to send notifications whenever its frame rectangle changes.
+        //
+        // We explicitly do this _after_ setting the view as the content view of the window, to
+        // avoid a resize event when creating the window.
+        view.setPostsFrameChangedNotifications(true);
+        // `setPostsFrameChangedNotifications` posts the notification immediately, so register the
+        // observer _after_, again so that the event isn't triggered initially.
+        let notification_center = unsafe { NSNotificationCenter::defaultCenter() };
+        unsafe {
+            notification_center.addObserver_selector_name_object(
+                &view,
+                sel!(viewFrameDidChangeNotification:),
+                Some(NSViewFrameDidChangeNotification),
+                Some(&view),
+            )
+        }
+
         if attrs.transparent {
             window.setOpaque(false);
             // See `set_transparent` for details on why we do this.