Fix HeadlessWindowImpl.Position does not persist new value (#17103)

* Fix HeadlessWindowImpl.Position does not persist new value

* Create unit-test for 17071 fix

* Fix CI errors

---------

Co-authored-by: Max Katz <maxkatz6@outlook.com>

src/Headless/Avalonia.Headless/HeadlessWindowImpl.cs

@@ -362,7 +362,8 @@ namespace Avalonia.Headless
 
         void IWindowImpl.Move(PixelPoint point)
         {
-
+            Position = point;
+            PositionChanged?.Invoke(point);
         }
 
         public IPopupImpl? CreatePopup()

tests/Avalonia.Headless.UnitTests/InputTests.cs

@@ -58,6 +58,19 @@ public class InputTests
 
         Assert.True(buttonClicked);
     }
+    
+#if NUNIT
+    [AvaloniaTest, Timeout(10000)]
+#elif XUNIT
+    [AvaloniaFact(Timeout = 10000)]
+#endif
+    public void Change_Window_Position()
+    {
+        var newWindowPosition = new PixelPoint(100, 150);
+        _window.Position = newWindowPosition;
+        _window.Show();
+        Assert.True(_window.Position == newWindowPosition);
+    }
 
 #if NUNIT
     [TearDown]