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