Fix some confusing uses of const

There are a few places where we have

    typedef struct FooData { ... } FooData;
    typedef FooData *Foo;

and then function declarations with

    bar(const Foo x)

which isn't incorrect but probably meant

    bar(const FooData *x)

meaning that the thing x points to is immutable, not x itself.

This patch makes those changes where appropriate.  In one
case (execGrouping.c), the thing being pointed to was not immutable,
so in that case remove the const altogether, to avoid further
confusion.

Co-authored-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://www.postgresql.org/message-id/CAEoWx2m2E0xE8Kvbkv31ULh_E%2B5zph-WA_bEdv3UR9CLhw%2B3vg%40mail.gmail.com
Discussion: https://www.postgresql.org/message-id/CAEoWx2kTDz%3Db6T2xHX78vy_B_osDeCC5dcTCi9eG0vXHp5QpdQ%40mail.gmail.com

src/include/access/gin_private.h

@@ -333,7 +333,7 @@ typedef struct GinScanKeyData
 	bool		curItemMatches;
 	bool		recheckCurItem;
 	bool		isFinished;
-}			GinScanKeyData;
+} GinScanKeyData;
 
 typedef struct GinScanEntryData
 {
@@ -478,7 +478,7 @@ extern void ginInsertCleanup(GinState *ginstate, bool full_clean,
 
 /* ginpostinglist.c */
 
-extern GinPostingList *ginCompressPostingList(const ItemPointer ipd, int nipd,
+extern GinPostingList *ginCompressPostingList(const ItemPointerData *ipd, int nipd,
 											  int maxsize, int *nwritten);
 extern int	ginPostingListDecodeAllSegmentsToTbm(GinPostingList *ptr, int len, TIDBitmap *tbm);
 

src/include/nodes/tidbitmap.h

@@ -85,7 +85,7 @@ extern void tbm_free(TIDBitmap *tbm);
 extern void tbm_free_shared_area(dsa_area *dsa, dsa_pointer dp);
 
 extern void tbm_add_tuples(TIDBitmap *tbm,
-						   const ItemPointer tids, int ntids,
+						   const ItemPointerData *tids, int ntids,
 						   bool recheck);
 extern void tbm_add_page(TIDBitmap *tbm, BlockNumber pageno);