[MacOS] fix small memory leak. base.Dispose so that _nativeControlHos…

…t and _mouse are disposed correctly. (#17783)

src/Avalonia.Native/WindowImplBase.cs

@@ -78,8 +78,7 @@ public override void SetFrameThemeVariant(PlatformThemeVariant themeVariant)
         public override void Dispose()
         {
             Native?.Close();
-            Native?.Dispose();
-            _handle = null;
+            base.Dispose();
         }
 
         public virtual void Show(bool activate, bool isDialog)