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/nodes/equalfuncs.c

@@ -414,6 +414,12 @@ _equalScalarArrayOpExpr(const ScalarArrayOpExpr *a, const ScalarArrayOpExpr *b)
 		b->hashfuncid != 0)
 		return false;
 
+	/* Likewise for the negfuncid */
+	if (a->negfuncid != b->negfuncid &&
+		a->negfuncid != 0 &&
+		b->negfuncid != 0)
+		return false;
+
 	COMPARE_SCALAR_FIELD(useOr);
 	COMPARE_SCALAR_FIELD(inputcollid);
 	COMPARE_NODE_FIELD(args);