fix: Optimize projections in recursive CTEs

[nuno-faria]

Which issue does this PR close?

• Closes Optimize projections causes recursive CTEs to fail #22249.
• Closes Projection pushdown on Recursive CTEs with nested subqueries #17853.

Rationale for this change

Optimize projections for the static and recursive terms of recursive CTEs just like regular subqueries. The previous implementation optimized projections based on the outer columns, which could cause bugs.

This new implementation still ensures that #16684 remains fixed.

What changes are included in this PR?

• Updated optimize_projections to be applied to the static and recursive terms of a recursive query.
• Updated and added tests.

Are these changes tested?

Yes.

Are there any user-facing changes?

Maybe if the user relied on projections being pushed down from the outer query to the recursive CTE, but this can be fixed by removing those unnecessary projections directly in the CTE.

[nuno-faria]

This test was very similar to the now named recursive_cte_outer_projection_pushdown.

[nuno-faria]

Projection is now optimized here.

[nuno-faria]

Same here.

[Omega359]

This PR tests the recursive CTE projection fix for UNION ALL, but not for recursive UNION where an outer-unselected column still affects distinctness. This matters because pruning that column would collapse distinct rows incorrectly. The test is below.

# Keep columns that are not selected by the outer query, but still affect
# recursive UNION distinctness.
query I
with recursive t(k, v) as (
  select 1 k, 10 v
  union
  select 2, 10 from t where v = 10
)
select v
from t
order by 1;
----
10
10

[nuno-faria]

Thanks @Omega359. I've added the union test as well.