pgsql: Standardize ItemIdData terminology.

Standardize ItemIdData terminology.

The term "item pointer" should not be used to refer to ItemIdData
variables, since that is needlessly ambiguous. Only
ItemPointerData/ItemPointer variables should be called item pointers.

To fix, establish the convention that ItemIdData variables should always
be referred to either as "item identifiers" or "line pointers". The
term "item identifier" already predominates in docs and translatable
messages, and so should be the preferred alternative there.

Discussion: https://postgr.es/m/CAH2-Wz=c=MZQjUzde3o9+2PLAPuHTpVZPPdYxN=E4ndQ2--8ew@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ae7291acbc5ae4c3751615177fc256f9f3399403

Modified Files
--------------
contrib/amcheck/verify_nbtree.c | 4 ++--
src/backend/access/heap/README.HOT | 10 +++++-----
src/backend/access/heap/heapam.c | 4 ++--
src/backend/access/heap/heapam_handler.c | 2 +-
src/backend/access/heap/pruneheap.c | 10 +++++-----
src/backend/access/heap/vacuumlazy.c | 6 +++---
src/backend/access/index/indexam.c | 26 --------------------------
src/backend/access/nbtree/nbtinsert.c | 2 +-
src/backend/access/spgist/spgvacuum.c | 2 +-
src/backend/storage/page/bufpage.c | 26 +++++++++++++-------------
src/include/access/htup_details.h | 2 +-
src/include/access/itup.h | 2 +-
src/include/storage/bufpage.h | 16 ++++++++++------
src/include/storage/itemid.h | 13 +++++++------
14 files changed, 52 insertions(+), 73 deletions(-)