switch_to_blog() - flag for missing subsequent restore_current_blog()

## Describe the solution you'd like

From https://github.com/Automattic/VIP-Coding-Standards/pull/649#discussion_r606174833, it would be worth flagging that `restore_current_blog()` should be called subsequently (if not already).

## What code should be reported as a violation?

```
function switch_blog() {
$id = get_current_blog_id();

if ( $id === 2 ) {
return;
}

switch_to_blog( 2 );
}
```

## What code should *not* be reported as a violation?

```
function switch_blog() {
$id = get_current_blog_id();

if ( $id === 2 ) {
return;
}

switch_to_blog( 2 );
restore_current_blog();
}
```

找到处理 switch_to_blog() 的现有规则或 sniff，然后检查它如何确定一次调用是否成对。为 issue 中的两个示例添加覆盖：报告没有后续 restore_current_blog() 的 switch，不要报告已恢复的情况。

由索引模型根据 Issue 内容生成。