Enforce notebook cell title menu as proposed API

src/vs/workbench/api/common/menusExtensionPoint.ts

@@ -64,6 +64,7 @@ namespace schema {
 		switch (menuId) {
 			case MenuId.StatusBarWindowIndicatorMenu:
 			case MenuId.MenubarWebNavigationMenu:
+			case MenuId.NotebookCellTitle:
 				return true;
 		}
 		return false;