Alias selection and conflated results when the same alias name is projected multiple times before a subquery

When projection expressions define multiple aliases with the same name and project a subquery using that alias name, we don't match MySQL's behavior.

**Example Query:** `select 0 as a, 1 as a, (SELECT x from xy where x = a);`
**MySQL Results:** `{0, 1, 0}`
**GMS Results:** `{1, 1, 1}`

GMS currently chooses the second alias when it is referenced in the subquery, and the first column gets conflated with the second alias and returns incorrect results, too. This bug doesn't happen without the subquery projection expression, so seems likely that as part of manipulating the plan, we mess up the projection expressions.