pgsql: Move LSN waiting declarations and definitions to better place

Move LSN waiting declarations and definitions to better place

3c5db1d6b implemented the pg_wal_replay_wait() stored procedure.  Due to
the patch development history, the implementation resided in
src/backend/commands/waitlsn.c (src/include/commands/waitlsn.h for headers).

014f9f34d moved pg_wal_replay_wait() itself to
src/backend/access/transam/xlogfuncs.c near to the WAL-manipulation functions.
But most of the implementation stayed in place.

The code in src/backend/commands/waitlsn.c has nothing to do with commands,
but is related to WAL.  So, this commit moves this code into
src/backend/access/transam/xlogwait.c (src/include/access/xlogwait.h for
headers).

Reported-by: Peter Eisentraut
Discussion: https://postgr.es/m/18c0fa64-0475-415e-a1bd-665d922c5201%40eisentraut.org
Reviewed-by: Pavel Borisov

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5035172e4ab58e4e8eef1bc60b0712fc59e0be31

Modified Files
--------------
src/backend/access/transam/Makefile                           |  3 ++-
src/backend/access/transam/meson.build                        |  1 +
src/backend/access/transam/xact.c                             |  2 +-
src/backend/access/transam/xlog.c                             |  2 +-
src/backend/access/transam/xlogfuncs.c                        |  2 +-
src/backend/access/transam/xlogrecovery.c                     |  2 +-
src/backend/{commands/waitlsn.c => access/transam/xlogwait.c} |  6 +++---
src/backend/commands/Makefile                                 |  3 +--
src/backend/commands/meson.build                              |  1 -
src/backend/storage/ipc/ipci.c                                |  2 +-
src/backend/storage/lmgr/proc.c                               |  2 +-
src/include/{commands/waitlsn.h => access/xlogwait.h}         | 10 +++++-----
12 files changed, 18 insertions(+), 18 deletions(-)