pgsql: Mark ItemPointer arguments as const in tuple/table lock function

Mark ItemPointer arguments as const in tuple/table lock functions

The functions LockTuple, ConditionalLockTuple, UnlockTuple, and
XactLockTableWait take an ItemPointer argument that they do not
modify, so the argument can be const-qualified to better convey intent
and allow the compiler to enforce immutability.

Author: Chao Li <li.evan.chao@gmail.com>
Discussion:
https://www.postgresql.org/message-id/flat/CAEoWx2m9e4rECHBwpRE4%2BGCH%2BpbYZXLh2f4rB1Du5hDfKug%2BOg%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/991295f387a6a453fe061831bcc36294989fe77b

Modified Files
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src/backend/storage/lmgr/lmgr.c | 10 +++++-----
src/include/storage/lmgr.h      |  8 ++++----
2 files changed, 9 insertions(+), 9 deletions(-)