Hack to reset focus when context menu closed.

Including a fix to `FocusManager` to ensure that it doesn't try to set focus to an invisble focus scope. Fixes #3738.

src/Avalonia.Controls/ContextMenu.cs

@@ -21,6 +21,7 @@ namespace Avalonia.Controls
             new FuncTemplate<IPanel>(() => new StackPanel { Orientation = Orientation.Vertical });
         private Popup _popup;
         private bool _attachedToControl;
+        private IInputElement _previousFocus;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ContextMenu"/> class.
@@ -150,6 +151,7 @@ namespace Avalonia.Controls
 
         private void PopupOpened(object sender, EventArgs e)
         {
+            _previousFocus = FocusManager.Instance?.Current;
             Focus();
         }
 
@@ -171,6 +173,9 @@ namespace Avalonia.Controls
                 ((ISetLogicalParent)_popup).SetParent(null);
             }
 
+            // HACK: Reset the focus when the popup is closed. We need to fix this so it's automatic.
+            FocusManager.Instance?.Focus(_previousFocus);
+
             RaiseEvent(new RoutedEventArgs
             {
                 RoutedEvent = MenuClosedEvent,

src/Avalonia.Input/FocusManager.cs

@@ -168,7 +168,7 @@ namespace Avalonia.Input
             {
                 var scope = control as IFocusScope;
 
-                if (scope != null)
+                if (scope != null && control.VisualRoot?.IsVisible == true)
                 {
                     yield return scope;
                 }