Re-disallow Memoize for parameterized nested loops with join filters

This was previously fixed in 9e215378d but got broken again as a result
of 2489d76c4.  It seems that commit causes ppi_clauses to contain
duplicate clauses and it's no longer safe to check the list_length of
that list to determine if there are join conditions other than what's
mentioned in ppi_clauses.

Here we adjust the check to count the distinct rinfo_serial mentioned in
ppi_clauses.  We expect that extra->restrictlist won't have duplicate
rinfo_serials.

Reported-by: Amadeo Gallardo
Author: Richard Guo
Discussion: https://postgr.es/m/CADFREbW-BLJd7-a5J%2B5wjVumeFG1ByXiSOFzMtkmY_SDWckTxw%40mail.gmail.com
Backpatch-through: 16, where 2489d76c4 was introduced.

src/backend/optimizer/path/joinpath.c

@@ -635,7 +635,7 @@ get_memoize_path(PlannerInfo *root, RelOptInfo *innerrel,
 	 */
 	if (extra->inner_unique &&
 		(inner_path->param_info == NULL ||
-		 list_length(inner_path->param_info->ppi_clauses) <
+		 bms_num_members(inner_path->param_info->ppi_serials) <
 		 list_length(extra->restrictlist)))
 		return NULL;