Use a hash table to speed up NOT IN(values)

Similar to 50e17ad28, which allowed hash tables to be used for IN clauses
with a set of constants, here we add the same feature for NOT IN clauses.

NOT IN evaluates the same as: WHERE a <> v1 AND a <> v2 AND a <> v3.
Obviously, if we're using a hash table we must be exactly equivalent to
that and return the same result taking into account that either side of
the condition could contain a NULL.  This requires a little bit of
special handling to make work with the hash table version.

When processing NOT IN, the ScalarArrayOpExpr's operator will be the <>
operator.  To be able to build and lookup a hash table we must use the
<>'s negator operator.  The planner checks if that exists and is hashable
and sets the relevant fields in ScalarArrayOpExpr to instruct the executor
to use hashing.

Author: David Rowley, James Coleman
Reviewed-by: James Coleman, Zhihong Yu
Discussion: https://postgr.es/m/CAApHDvoF1mum_FRk6D621edcB6KSHBi2+GAgWmioj5AhOu2vwQ@mail.gmail.com

src/backend/parser/parse_oper.c

@@ -895,6 +895,7 @@ make_scalar_array_op(ParseState *pstate, List *opname,
 	result->opno = oprid(tup);
 	result->opfuncid = opform->oprcode;
 	result->hashfuncid = InvalidOid;
+	result->negfuncid = InvalidOid;
 	result->useOr = useOr;
 	/* inputcollid will be set by parse_collate.c */
 	result->args = args;