pgsql: Fix some confusing uses of const

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

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/8ce795fcb70df7a8fdf3303eec0cfcd703b0d122

Modified Files
--------------
contrib/pg_surgery/heap_surgery.c       |  4 ++--
src/backend/access/gin/ginget.c         |  2 +-
src/backend/access/gin/ginpostinglist.c |  4 ++--
src/backend/executor/execGrouping.c     |  8 ++++----
src/backend/nodes/tidbitmap.c           |  2 +-
src/backend/utils/adt/tsvector_op.c     | 12 ++++++------
src/include/access/gin_private.h        |  4 ++--
src/include/nodes/tidbitmap.h           |  2 +-
src/tools/pgindent/typedefs.list        |  1 +
9 files changed, 20 insertions(+), 19 deletions(-)