app: [iOS] fix focus event for iOS 13.0+ with backward compatibility

UIScene notifications are the correct way to track window focus on
iOS 13.0+, because the Key Window API is scene-level on iOS 13.0+,
but we need to maintain support for iOS 12 and earlier.

Implementation strategy:
- iOS 13.0+: Use UIScene notifications (DidActivate/WillDeactivate)
- iOS 12 and earlier: Keep existing UIWindow notifications as fallback
- Add runtime version checks to select the appropriate API

Key changes in os_ios.m:
- Add @available(iOS 13.0, *) checks
- Register both notification types with conditional logic
- Ensure proper cleanup of observers when moving between windows

See: https://developer.apple.com/documentation/uikit/uiscene?language=objc

Fixes: https://lists.sr.ht/~eliasnaur/gio/%3CCAMAFT9Uyh_JWrkQQt+AmekJWFBqhZPsP_3ZxC1fUNB+=VGGorw@mail.gmail.com%3E
Signed-off-by: CoyAce <akeycoy@gmail.com>
Signed-off-by: Elias Naur <mail@eliasnaur.com>

Author: CoyAce

app/os.go

@@ -47,7 +47,7 @@ type Config struct {
 	Decorated bool
 	// TopMost windows render above all other non-top-most windows.
 	TopMost bool
-	// Focused reports whether has the keyboard focus.
+	// Focused reports whether the window is focused.
 	Focused bool
 	// decoHeight is the height of the fallback decoration for platforms such
 	// as Wayland that may need fallback client-side decorations.

app/os_ios.m

@@ -134,23 +134,59 @@ + (Class)layerClass {
     return gio_layerClass();
 }
 - (void)willMoveToWindow:(UIWindow *)newWindow {
+	self.contentScaleFactor = newWindow.screen.nativeScale;
+    if (@available(iOS 13.0, *)) {
+        [self registerSceneNotifications:newWindow];
+    }else{
+        [self registerWindowNotifications:newWindow];
+    }
+}
+
+- (void)registerSceneNotifications:(UIWindow *)newWindow {
+        if (self.window != nil) {
+            [[NSNotificationCenter defaultCenter] removeObserver:self
+                                                  name:UISceneDidActivateNotification
+                                                  object:self.window.windowScene];
+            [[NSNotificationCenter defaultCenter] removeObserver:self
+                                                  name:UISceneWillDeactivateNotification
+                                                  object:self.window.windowScene];
+        }
+        [[NSNotificationCenter defaultCenter] addObserver:self
+                                              selector:@selector(onSceneDidActivate:)
+                                              name:UISceneDidActivateNotification
+                                              object:newWindow.windowScene];
+
+        [[NSNotificationCenter defaultCenter] addObserver:self
+                                              selector:@selector(onSceneWillDeactivate:)
+                                              name:UISceneWillDeactivateNotification
+                                              object:newWindow.windowScene];
+}
+
+- (void)onSceneDidActivate:(NSNotification *)note API_AVAILABLE(ios(13.0)){
+    onFocus(self.handle, YES);
+}
+
+- (void)onSceneWillDeactivate:(NSNotification *)note API_AVAILABLE(ios(13.0)){
+    onFocus(self.handle, NO);
+}
+
+- (void)registerWindowNotifications:(UIWindow *)newWindow {
 	if (self.window != nil) {
 		[[NSNotificationCenter defaultCenter] removeObserver:self
-														name:UIWindowDidBecomeKeyNotification
-													  object:self.window];
+											  name:UIWindowDidBecomeKeyNotification
+										      object:self.window];
 		[[NSNotificationCenter defaultCenter] removeObserver:self
-														name:UIWindowDidResignKeyNotification
-													  object:self.window];
+											  name:UIWindowDidResignKeyNotification
+											  object:self.window];
 	}
-	self.contentScaleFactor = newWindow.screen.nativeScale;
 	[[NSNotificationCenter defaultCenter] addObserver:self
-											 selector:@selector(onWindowDidBecomeKey:)
-												 name:UIWindowDidBecomeKeyNotification
-											   object:newWindow];
+										  selector:@selector(onWindowDidBecomeKey:)
+										  name:UIWindowDidBecomeKeyNotification
+										  object:newWindow];
 	[[NSNotificationCenter defaultCenter] addObserver:self
-											 selector:@selector(onWindowDidResignKey:)
-												 name:UIWindowDidResignKeyNotification
-											   object:newWindow];
+										  selector:@selector(onWindowDidResignKey:)
+										  name:UIWindowDidResignKeyNotification
+										  object:newWindow];
 }
 
 - (void)onWindowDidBecomeKey:(NSNotification *)note {