Improve flush_rewrite_rules warning

## What problem would the enhancement address for VIP?

Right now here's the rule that we see when you try to use `flush_rewrite_rules()`:

> 🚫 Error( severity 5 ): flush_rewrite_rules should not be used in any normal circumstances in the theme code (WordPressVIPMinimum.Functions.RestrictedFunctions.flush_rewrite_rules_flush_rewrite_rules).

I feel like adding more context here as to "why" would be helpful, and also adding cases where this might be appropriate? For example, what about in a plugin activation/deactivation hook?

## Describe the solution you'd like

1. Why should you not use it
2. When it might be ok to use
3. What the effect of using it would have
4. Link to a doc on docs.wpvip.com to more details

找到发出 flush_rewrite_rules 警告的 PHP_CodeSniffer 规则，并查看其现有消息和相关文档。更新警告，解释为什么不建议使用该函数、何时适合使用激活或停用钩子、它的影响，以及相关的 docs.wpvip.com 链接；如果存在该规则的测试，请进行验证。

由索引模型根据 Issue 内容生成。