Fix PG 17 [NOT] NULL optimization bug for domains

Fix PG 17 [NOT] NULL optimization bug for domains

A PG 17 optimization allowed columns with NOT NULL constraints to skip
table scans for IS NULL queries, and to skip IS NOT NULL checks for IS
NOT NULL queries.  This didn't work for domain types, since domain types
don't follow the IS NULL/IS NOT NULL constraint logic.  To fix, disable
this optimization for domains for PG 17+.

Reported-by: Jan Behrens
Diagnosed-by: Tom Lane
Discussion: https://postgr.es/m/Z37p0paENWWUarj-@momjian.us

Backpatch-through: 17