Fixes/windows back requested (#21207)

* feat: Add test verifyig BackRequested not working

* fix: Use InputRoot not this when checking for back requested

src/Avalonia.Controls/TopLevel.cs

@@ -286,7 +286,7 @@ namespace Avalonia.Controls
 
             _backGestureSubscription = _inputManager?.PreProcess.Subscribe(e =>
             {
-                if (e.Root != this)
+                if (e.Root != InputRoot)
                     return;
 
                 bool backRequested = false;

tests/Avalonia.Controls.UnitTests/TopLevelTests.cs

@@ -253,6 +253,36 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void XButton1Down_Should_Raise_BackRequested()
+        {
+            // Regression test: prior to this fix, the PreProcess subscription compared
+            // e.Root against 'this' (the TopLevel/Window), but e.Root is set to the
+            // PresentationSource (the IInputRoot), not the Window itself. The comparison
+            // always failed so BackRequested was never raised for XButton1Down.
+            var services = TestServices.StyledWindow.With(inputManager: new InputManager());
+
+            using (UnitTestApplication.Start(services))
+            {
+                var impl = CreateMockTopLevelImpl(true);
+                var target = new TestTopLevel(impl.Object);
+
+                var raised = false;
+                target.BackRequested += (_, _) => raised = true;
+
+                var mouseDevice = new MouseDevice(new Pointer(0, PointerType.Mouse, true));
+                impl.Object.Input!(new RawPointerEventArgs(
+                    mouseDevice,
+                    timestamp: 0,
+                    target.InputRoot,
+                    RawPointerEventType.XButton1Down,
+                    new RawPointerPoint { Position = default },
+                    RawInputModifiers.None));
+
+                Assert.True(raised);
+            }
+        }
+
         [Fact]
         public void TopLevel_Should_Unfocus_When_Impl_Focus_Is_Lost()
         {