Add integration tests for checking window sizes on launch when client is extended. (#13871)

* win32 - fix client size update when window is opened with extended client area

* add tests for extended client window show size

tests/Avalonia.IntegrationTests.Appium/WindowTests.cs

@@ -205,6 +205,17 @@ namespace Avalonia.IntegrationTests.Appium
             }
         }
 
+        [Fact]
+        public void Extended_Client_Window_Shows_With_Requested_Size()
+        {
+            var clientSize = new Size(400, 400);
+            using var window = OpenWindow(clientSize, ShowWindowMode.NonOwned, WindowStartupLocation.CenterScreen, extendClientArea: true);
+            var windowState = _session.FindElementByAccessibilityId("CurrentWindowState");
+            var current = GetWindowInfo();
+
+            Assert.Equal(current.ClientSize, clientSize);
+        }
+
         [Fact]
         public void TransparentWindow()
         {