Make the order of the header file includes consistent in backend modules.

Similar to commits 7e735035f2 and dddf4cdc33, this commit makes the order
of header file inclusion consistent for backend modules.

In the passing, removed a couple of duplicate inclusions.

Author: Vignesh C
Reviewed-by: Kuntal Ghosh and Amit Kapila
Discussion: https://postgr.es/m/CALDaNm2Sznv8RR6Ex-iJO6xAdsxgWhCoETkaYX=+9DW3q0QCfA@mail.gmail.com

src/backend/optimizer/util/pathnode.c

@@ -16,8 +16,8 @@
 
 #include <math.h>
 
-#include "miscadmin.h"
 #include "foreign/fdwapi.h"
+#include "miscadmin.h"
 #include "nodes/extensible.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/appendinfo.h"
@@ -35,7 +35,6 @@
 #include "utils/memutils.h"
 #include "utils/selfuncs.h"
 
-
 typedef enum
 {
 	COSTS_EQUAL,				/* path costs are fuzzily equal */

src/backend/optimizer/util/plancat.c

@@ -20,9 +20,9 @@
 #include "access/genam.h"
 #include "access/htup_details.h"
 #include "access/nbtree.h"
-#include "access/tableam.h"
 #include "access/sysattr.h"
 #include "access/table.h"
+#include "access/tableam.h"
 #include "access/transam.h"
 #include "access/xlog.h"
 #include "catalog/catalog.h"
@@ -40,9 +40,9 @@
 #include "optimizer/optimizer.h"
 #include "optimizer/plancat.h"
 #include "optimizer/prep.h"
-#include "partitioning/partdesc.h"
 #include "parser/parse_relation.h"
 #include "parser/parsetree.h"
+#include "partitioning/partdesc.h"
 #include "rewrite/rewriteManip.h"
 #include "statistics/statistics.h"
 #include "storage/bufmgr.h"
@@ -50,9 +50,8 @@
 #include "utils/lsyscache.h"
 #include "utils/partcache.h"
 #include "utils/rel.h"
-#include "utils/syscache.h"
 #include "utils/snapmgr.h"
-
+#include "utils/syscache.h"
 
 /* GUC parameter */
 int			constraint_exclusion = CONSTRAINT_EXCLUSION_PARTITION;