Merge pull request AvaloniaUI#7622 from pr8x/child-window-property2

Exposing `Window.ChildWindows` collection

Author: danwalmsley

src/Avalonia.Controls/Window.cs

@@ -255,6 +255,11 @@ public Window(IWindowImpl impl)
         [CanBeNull]
         public new IWindowImpl PlatformImpl => (IWindowImpl)base.PlatformImpl;
 
+        /// <summary>
+        /// Gets a collection of child windows owned by this window.
+        /// </summary>
+        public IReadOnlyList<Window> OwnedWindows => _children.Select(x => x.child).ToList();
+
         /// <summary>
         /// Gets or sets a value indicating how the window will size itself to fit its content.
         /// </summary>