Question on: `visit_expressions_mut` for alias expr

When I run `visit_expressions_mut` it works very well. However, I have no way to get to an alias expr, such as:

```sql
SELECT a.x, b.y AS myby, myfn(c.z) AS myfncall {
FROM t1
...
```
I pass the `projection` to `visit_expressions_mut` and I see the `CompoundIdentifier` and the `Function` expressions, but the alias rename does not come through. It seems like this is excluded, even though `ExprWithAlias` has a derive for `VisitorMut`. Is this intentional or a bug?

从 projection 上的 visit_expressions_mut 开始，检查 ExprWithAlias 的 VisitorMut derive 如何处理 alias 表达式。重现 SQL 示例，然后确定 alias 重命名是否按预期被访问；如果该行为是 bug，则添加或更新覆盖范围；payload 未指定文件或测试。

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