Which issue does this PR close?

• Closes IN subqueries can return incorrect results #21205.
• Closes Spurious error when subquery column alias clashes with outer query identifier #21206.

Rationale for this change

This PR fixes three separate bugs in query decorrelation:

1. When removing duplicate filters as part of pulling up IN subqueries, an operator precedence error meant that we would consider two filters to be duplicates even if they involved different operators (e.g., = and >).
2. When generating the CASE used to implement "count bug" handling, we referenced the subquery output column without qualifying it by the subquery alias. This could result in name-collisions with unrelated identifiers in the parent query.
3. After generating the CASE used for "count bug" handling, we rewrote the parent query to replace references to the subquery output column with the generated CASE expression. This rewrite only matched on unqualified column name only, which meant that unrelated parent query identifiers that happened to share the same column name as subquery aggregate aliases could been rewritten by mistake.

The first and third issues could result in incorrect query results; the second would only cause spurious errors, as far as I can see.

What changes are included in this PR?

• Fix all three bugs
• Add SLT tests
• Add a debug_assert! to document/check that remove_duplicated_filter is called with a commutative operator

Are these changes tested?

Yes.

Are there any user-facing changes?

No, except in the sense that they fix user-visible bugs.