iOS: fix universal link activation with scenes (#20752)

src/iOS/Avalonia.iOS/AvaloniaAppDelegate.cs

@@ -12,7 +12,12 @@ namespace Avalonia.iOS
         event EventHandler<ActivatedEventArgs> Deactivated;
     }
 
-    public class AvaloniaAppDelegate<TApp> : UIResponder, IUIApplicationDelegate, IAvaloniaAppDelegate
+    internal interface IAvaloniaAppInternalDelegate
+    {
+        bool ContinueUserActivity(NSUserActivity userActivity);
+    }
+
+    public class AvaloniaAppDelegate<TApp> : UIResponder, IUIApplicationDelegate, IAvaloniaAppDelegate, IAvaloniaAppInternalDelegate
         where TApp : Application, new()
     {
         private EventHandler<ActivatedEventArgs>? _onActivated, _onDeactivated;
@@ -104,7 +109,13 @@ namespace Avalonia.iOS
         [Export("application:continueUserActivity:restorationHandler:")]
         public bool ContinueUserActivity(UIApplication application, NSUserActivity userActivity, UIApplicationRestorationHandler completionHandler)
         {
-            if (userActivity.ActivityType == NSUserActivityType.BrowsingWeb && Uri.TryCreate(userActivity.WebPageUrl?.ToString(), UriKind.RelativeOrAbsolute, out var uri))
+            return ((IAvaloniaAppInternalDelegate)this).ContinueUserActivity(userActivity);
+        }
+
+        bool IAvaloniaAppInternalDelegate.ContinueUserActivity(NSUserActivity userActivity)
+        {
+            if (userActivity.ActivityType == NSUserActivityType.BrowsingWeb &&
+                Uri.TryCreate(userActivity.WebPageUrl?.ToString(), UriKind.RelativeOrAbsolute, out var uri))
             {
                 // Activation using a univeral link or web browser-to-native app Handoff
                 _onActivated?.Invoke(this, new ProtocolActivatedEventArgs(uri));

src/iOS/Avalonia.iOS/AvaloniaSceneDelegate.cs

@@ -24,6 +24,13 @@ internal sealed class AvaloniaSceneDelegate : UIResponder, IUIWindowSceneDelegat
         Window.MakeKeyAndVisible();
     }
 
+    [Export("scene:continueUserActivity:")]
+    public void ContinueUserActivity(UIScene scene, NSUserActivity userActivity)
+    {
+        var appDelegate = UIApplication.SharedApplication.Delegate as IAvaloniaAppInternalDelegate;
+        appDelegate?.ContinueUserActivity(userActivity);
+    }
+
     internal static void InitWindow(UIWindow window, SingleViewLifetime lifetime)
     {
         var view = new AvaloniaView();