Reduce allocations when creating weak event subscribers.

src/Avalonia.Base/Utilities/IWeakEventSubscriber.cs

@@ -11,7 +11,7 @@ public interface IWeakEventSubscriber<in TEventArgs> where TEventArgs : EventArg
     void OnEvent(object? sender, WeakEvent ev, TEventArgs e);
 }
 
-public class WeakEventSubscriber<TEventArgs> : IWeakEventSubscriber<TEventArgs> where TEventArgs : EventArgs 
+public sealed class WeakEventSubscriber<TEventArgs> : IWeakEventSubscriber<TEventArgs> where TEventArgs : EventArgs 
 {
     public event Action<object?, WeakEvent, TEventArgs>? Event;
 
@@ -19,4 +19,21 @@ public class WeakEventSubscriber<TEventArgs> : IWeakEventSubscriber<TEventArgs>
     {
         Event?.Invoke(sender, ev, e);
     }
-}
+}
+
+public sealed class TargetWeakEventSubscriber<TTarget, TEventArgs> : IWeakEventSubscriber<TEventArgs> where TEventArgs : EventArgs
+{
+    private readonly TTarget _target;
+    private readonly Action<TTarget, object?, WeakEvent, TEventArgs> _dispatchFunc;
+
+    public TargetWeakEventSubscriber(TTarget target, Action<TTarget, object?, WeakEvent, TEventArgs> dispatchFunc)
+    {
+        _target = target;
+        _dispatchFunc = dispatchFunc;
+    }
+
+    void IWeakEventSubscriber<TEventArgs>.OnEvent(object? sender, WeakEvent ev, TEventArgs e)
+    {
+        _dispatchFunc(_target, sender, ev, e);
+    }
+}

src/Avalonia.Base/Visual.cs

@@ -108,7 +108,7 @@ namespace Avalonia
         private IRenderRoot? _visualRoot;
         private IVisual? _visualParent;
         private bool _hasMirrorTransform;
-        private WeakEventSubscriber<EventArgs>? _affectsRenderWeakSubscriber;
+        private TargetWeakEventSubscriber<Visual, EventArgs>? _affectsRenderWeakSubscriber;
 
         /// <summary>
         /// Initializes static members of the <see cref="Visual"/> class.
@@ -383,11 +383,11 @@ namespace Avalonia
                     {
                         if (sender._affectsRenderWeakSubscriber == null)
                         {
-                            sender._affectsRenderWeakSubscriber = new WeakEventSubscriber<EventArgs>();
-                            sender._affectsRenderWeakSubscriber.Event += delegate
-                            {
-                                sender.InvalidateVisual();
-                            };
+                            sender._affectsRenderWeakSubscriber = new TargetWeakEventSubscriber<Visual, EventArgs>(
+                                sender, static (target, _, _, _) =>
+                                {
+                                    target.InvalidateVisual();
+                                });
                         }
                         InvalidatedWeakEvent.Subscribe(newValue, sender._affectsRenderWeakSubscriber);
                     }