Trying to fix flaky window decorations tests. (#16597)

Toggling the window decorations can cause the window to be moved off screen, causing integration test failures. Until this bug is fixed, detect this and move the window to the screen origin. See #11411.

samples/IntegrationTestApp/MainWindow.axaml.cs

@@ -1,4 +1,6 @@
+using System;
 using System.Collections.Generic;
+using Avalonia;
 using Avalonia.Controls;
 using IntegrationTestApp.Models;
 using IntegrationTestApp.Pages;
@@ -20,6 +22,7 @@ namespace IntegrationTestApp
 
             DataContext = viewModel;
             AppOverlayPopups.Text = Program.OverlayPopups ? "Overlay Popups" : "Native Popups";
+            PositionChanged += OnPositionChanged;
         }
 
         private MainWindowViewModel? ViewModel => (MainWindowViewModel?)DataContext;
@@ -53,6 +56,22 @@ namespace IntegrationTestApp
                 PagerContent.Child = page.CreateContent();
         }
 
+        private void OnPositionChanged(object? sender, PixelPointEventArgs e)
+        {
+            // HACK: Toggling the window decorations can cause the window to be moved off screen, 
+            // causing test failures. Until this bug is fixed, detect this and move the window
+            // to the screen origin. See #11411.
+            if (Screens.ScreenFromWindow(this) is { } screen)
+            {
+                var bounds = new PixelRect(
+                    e.Point,
+                    PixelSize.FromSize(ClientSize, DesktopScaling));
+
+                if (!screen.WorkingArea.Contains(bounds))
+                    Position = screen.WorkingArea.Position;
+            }
+        }
+
         private static IEnumerable<Page> CreatePages()
         {
             return