Fix mishandling of OLD/NEW references in subqueries in rule actions.

Fix mishandling of OLD/NEW references in subqueries in rule actions.

If a rule action contains a subquery that refers to columns from OLD
or NEW, then those are really lateral references, and the planner will
complain if it sees such things in a subquery that isn't marked as
lateral. However, at rule-definition time, the user isn't required to
mark the subquery with LATERAL, and so it can fail when the rule is
used.

Fix this by marking such subqueries as lateral in the rewriter, at the
point where they're used.

Dean Rasheed and Tom Lane, per report from Alexander Lakhin.
Back-patch to all supported branches.

Discussion: https://postgr.es/m/5e09da43-aaba-7ea7-0a51-a2eb981b058b%40gmail.com