Reuse aggregate-derived join domains as detail-side payloads

[pentschev]

This extends join_filter_pushdown to recognize when an aggregate-derived join domain can be reused as the payload for a later detail-side join input.

The motivating case is PDSH Q18. The query computes the set of l_orderkey values whose sum(l_quantity) > 300, and current planning can already use that result as a semi-join domain to filter orders. However, the final orders x lineitem join still reads the raw lineitem detail side again.

With this change, when the aggregate-derived domain is known to contain the join key and the payload columns needed by the later join, the planner can reuse that derived domain to feed the detail side as well. The original full join is still preserved, so the rewrite is a row-reduction optimization rather than a semantic shortcut.

Q18 plan before, relevant subtree

JOIN Inner ('o_orderkey',) ('l_orderkey',)
  JOIN Semi ('o_orderkey',) ('l_orderkey',)
    STREAMINGSCAN orders
    FILTER (sum_quantity > 300.0)
      GROUPBY ('l_orderkey',)
        STREAMINGSCAN lineitem ('l_orderkey', 'l_quantity')
  STREAMINGSCAN lineitem ('l_orderkey', 'l_quantity')

Q18 plan after, relevant subtree

JOIN Inner ('o_orderkey',) ('l_orderkey',)
  JOIN Semi ('o_orderkey',) ('l_orderkey',)
    STREAMINGSCAN orders
    FILTER (sum_quantity > 300.0)
      GROUPBY ('l_orderkey',)
        STREAMINGSCAN lineitem ('l_orderkey', 'l_quantity')
  FILTER BooleanFunction ('l_orderkey', 'l_quantity')
    SELECT ('l_orderkey', 'l_quantity')
      FILTER (sum_quantity > 300.0)
        GROUPBY ('l_orderkey',)
          STREAMINGSCAN lineitem ('l_orderkey', 'l_quantity')

Materially, this reduces Q18 memory pressure and improves runtime by avoiding the final unfiltered detail-side lineitem input. In the latest standalone validation, the full SF30K Q1-Q22 workflow completed successfully on 6xNVL4 nodes with validation passing in 146s lukewarm/128s hot.

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