bool 如果选择保存此类场景，则返回 true，如果按下 Cancel，则返回 false。
询问您是否要保存修改后的一个或多个场景。
In some cases, you might want to call this function before opening another Scene or creating a new Scene. A return value of true indicates that you may continue. A return value of false indicates that the user cancelled the operation and you should not Open another Scene.