WindowServer: Add support for default MenuItem

This allows marking a MenuItem as a default action, e.g. in a
context menu for an action that reflects what e.g. a double click
would perform.

Also enhance the window menu to mark the close action as the
default, and when double clicked perform that action.

Fixes #1289

Services/WindowServer/ClientConnection.cpp

@@ -648,7 +648,7 @@ void ClientConnection::handle(const Messages::WindowServer::WM_PopupWindowMenu&
         return;
     }
     auto& window = *(*it).value;
-    window.popup_window_menu(message.screen_position());
+    window.popup_window_menu(message.screen_position(), WindowMenuDefaultAction::BasedOnWindowState);
 }
 
 void ClientConnection::handle(const Messages::WindowServer::WM_StartWindowResize& request)