Save PathTargets for distinct/ordered relations in root->upper_targets[].

For the convenience of extensions, we previously only saved PathTargets
for grouped, window, and final relations in root->upper_targets[] in
grouping_planner().  To improve the convenience, save PathTargets for
distinct and ordered relations as well.

Author: Antonin Houska, with an additional change by me
Discussion: https://postgr.es/m/10994.1549559088@localhost

src/backend/optimizer/plan/planner.c

@@ -2035,6 +2035,8 @@ grouping_planner(PlannerInfo *root, bool inheritance_update,
 		 * of the corresponding upperrels might not be needed for this query.
 		 */
 		root->upper_targets[UPPERREL_FINAL] = final_target;
+		root->upper_targets[UPPERREL_ORDERED] = final_target;
+		root->upper_targets[UPPERREL_DISTINCT] = sort_input_target;
 		root->upper_targets[UPPERREL_WINDOW] = sort_input_target;
 		root->upper_targets[UPPERREL_GROUP_AGG] = grouping_target;