pgsql: Mark ItemPointer arguments as const throughout

Mark ItemPointer arguments as const throughout

This is a follow up 991295f.  I searched over src/ and made all
ItemPointer arguments as const as much as possible.

Note: We cut out from the original patch the pieces that would have
created incompatibilities in the index or table AM APIs.  Those could
be considered separately.

Author: Chao Li <li.evan.chao@gmail.com>
Discussion: https://www.postgresql.org/message-id/CAEoWx2nBaypg16Z5ciHuKw66pk850RFWw9ACS2DqqJ_AkKeRsw%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e1ac846f3d2836dcfa0ad15310e28d0a0b495500

Modified Files
--------------
src/backend/access/common/tidstore.c       |  2 +-
src/backend/access/hash/hashsort.c         |  2 +-
src/backend/access/heap/heapam.c           | 34 +++++++++++++++---------------
src/backend/access/nbtree/nbtdedup.c       |  2 +-
src/backend/access/nbtree/nbtsearch.c      |  4 ++--
src/backend/access/nbtree/nbtsort.c        |  4 ++--
src/backend/access/nbtree/nbtsplitloc.c    |  4 ++--
src/backend/access/spgist/spgdoinsert.c    |  2 +-
src/backend/access/spgist/spgutils.c       |  2 +-
src/backend/access/spgist/spgvacuum.c      |  2 +-
src/backend/catalog/indexing.c             |  6 +++---
src/backend/executor/execIndexing.c        |  8 +++----
src/backend/storage/lmgr/predicate.c       |  8 +++----
src/backend/utils/adt/tid.c                |  6 +++---
src/backend/utils/sort/tuplesortvariants.c |  2 +-
src/include/access/hash.h                  |  2 +-
src/include/access/heapam.h                | 12 +++++------
src/include/access/nbtree.h                |  2 +-
src/include/access/spgist_private.h        |  4 ++--
src/include/access/tidstore.h              |  2 +-
src/include/catalog/index.h                |  2 +-
src/include/catalog/indexing.h             |  6 +++---
src/include/executor/executor.h            |  4 ++--
src/include/storage/predicate.h            |  4 ++--
src/include/utils/tuplesort.h              |  2 +-
25 files changed, 64 insertions(+), 64 deletions(-)