C# 有关代码的展开与折叠

参考链接：

• https://www.cnblogs.com/eve612/p/13685489.html
• https://blog.csdn.net/weixin_44084713/article/details/117993652
• https://www.it1352.com/891715.html
• https://zhidao.baidu.com/question/128425816.html
• https://bbs.csdn.net/topics/230011540
• https://www.cnblogs.com/hnfxs/p/3184947.html
• https://www.cnblogs.com/lechenging/p/3533670.html