Add support for ordering by aliased column

In the following query

```sql
select a.col1, a.col2, string_overlap(a.col1, a.col2) as overlap order by string_overlap(a.col1, a.col2) desc
```

I would like to say `order by overlap desc` instead of repeating the function call. However, that does not seem to be supported. `string_overlap` is a custom python function here.