Make ContextMenu leak tests fail again.

By adding focus/input manager.

src/Avalonia.Controls/WindowBase.cs

@@ -255,7 +255,7 @@ namespace Avalonia.Controls
 
             if (scope != null)
             {
-                FocusManager.Instance.SetFocusScope(scope);
+                FocusManager.Instance?.SetFocusScope(scope);
             }
 
             IsActive = true;

tests/Avalonia.LeakTests/ControlTests.cs

@@ -5,6 +5,7 @@ using System.Runtime.Remoting.Contexts;
 using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using Avalonia.Diagnostics;
+using Avalonia.Input;
 using Avalonia.Layout;
 using Avalonia.Media;
 using Avalonia.Platform;
@@ -441,6 +442,10 @@ namespace Avalonia.LeakTests
                 }
 
                 var window = new Window();
+                window.Show();
+
+                Assert.Same(window, FocusManager.Instance.Current);
+
                 BuildAndShowContextMenu(window);
                 BuildAndShowContextMenu(window);
 
@@ -453,7 +458,10 @@ namespace Avalonia.LeakTests
 
         private IDisposable Start()
         {
-            return UnitTestApplication.Start(TestServices.StyledWindow);
+            return UnitTestApplication.Start(TestServices.StyledWindow.With(
+                focusManager: new FocusManager(),
+                keyboardDevice: () => new KeyboardDevice(),
+                inputManager: new InputManager()));
         }
 
         private class Node

tests/Avalonia.UnitTests/MockWindowingPlatform.cs

@@ -21,6 +21,10 @@ namespace Avalonia.UnitTests
         {
             var win = Mock.Of<IWindowImpl>(x => x.Scaling == 1);
             var mock = Mock.Get(win);
+            mock.Setup(x => x.Show()).Callback(() =>
+            {
+                mock.Object.Activated?.Invoke();
+            });
             mock.Setup(x => x.CreatePopup()).Returns(() =>
             {
                 if (popupImpl != null)