[FancyZonesEditor]: Grid Editor keyboard control (#12969)

- Ctrl+Tab to switch between zones and layout overlay window
- Tab to focus between grid zones and resizers
- While resizer is focused: arrows to move it; Del to remove it
- While zone is focused: (Shift)+S to split it horizontally/vertically

src/modules/fancyzones/editor/FancyZonesEditor/Overlay.cs

@@ -253,10 +253,19 @@ namespace FancyZonesEditor
 
         public void FocusEditor()
         {
-            if (_editorLayout != null && _editorLayout is CanvasEditor canvasEditor)
+            if (_editorLayout == null)
+            {
+                return;
+            }
+
+            if (_editorLayout is CanvasEditor canvasEditor)
             {
                 canvasEditor.FocusZone();
             }
+            else if (_editorLayout is GridEditor gridEditor)
+            {
+                gridEditor.FocusZone();
+            }
         }
 
         public void FocusEditorWindow()