pgsql: Split xlog.c into xlog.c and xlogrecovery.c.

Split xlog.c into xlog.c and xlogrecovery.c.

This moves the functions related to performing WAL recovery into the new
xlogrecovery.c source file, leaving xlog.c responsible for maintaining
the WAL buffers, coordinating the startup and switch from recovery to
normal operations, and other miscellaneous stuff that have always been in
xlog.c.

Reviewed-by: Andres Freund, Kyotaro Horiguchi, Robert Haas
Discussion: https://www.postgresql.org/message-id/a31f27b4-a31d-f976-6217-2b03be646ffa%40iki.fi

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/70e81861fadd9112fa2d425c762e163910a4ee52

Modified Files
--------------
contrib/pg_prewarm/autoprewarm.c               |    1 +
src/backend/access/transam/Makefile            |    1 +
src/backend/access/transam/xact.c              |    1 +
src/backend/access/transam/xlog.c              | 4623 ++----------------------
src/backend/access/transam/xlogfuncs.c         |    2 +-
src/backend/access/transam/xlogrecovery.c      | 4537 +++++++++++++++++++++++
src/backend/access/transam/xlogutils.c         |    6 +-
src/backend/postmaster/checkpointer.c          |    1 +
src/backend/postmaster/postmaster.c            |    1 +
src/backend/postmaster/startup.c               |    1 +
src/backend/replication/logical/logicalfuncs.c |    1 +
src/backend/replication/slotfuncs.c            |    1 +
src/backend/replication/walreceiver.c          |    1 +
src/backend/replication/walreceiverfuncs.c     |    1 +
src/backend/replication/walsender.c            |    1 +
src/backend/storage/ipc/ipci.c                 |    3 +
src/backend/storage/ipc/standby.c              |    1 +
src/backend/storage/sync/sync.c                |    1 +
src/backend/utils/misc/guc.c                   |    1 +
src/include/access/xlog.h                      |   87 +-
src/include/access/xlogrecovery.h              |  157 +
src/tools/pgindent/typedefs.list               |    2 +
22 files changed, 4982 insertions(+), 4449 deletions(-)