pgsql: Run checkpointer and bgwriter in crash recovery.

Run checkpointer and bgwriter in crash recovery.

Start up the checkpointer and bgwriter during crash recovery (except in
--single mode), as we do for replication. This wasn't done back in
commit cdd46c76 out of caution. Now it seems like a better idea to make
the environment as similar as possible in both cases. There may also be
some performance advantages.

Reviewed-by: Robert Haas <robertmhaas(at)gmail(dot)com>
Reviewed-by: Aleksander Alekseev <aleksander(at)timescale(dot)com>
Tested-by: Jakub Wartak <Jakub(dot)Wartak(at)tomtom(dot)com>
Discussion: https://postgr.es/m/CA%2BhUKGJ8NRsqgkZEnsnRc2MFROBV-jCnacbYvtpptK2A9YYp9Q%40mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/7ff23c6d277d1d90478a51f0dd81414d343f3850

Modified Files
--------------
src/backend/access/transam/xlog.c | 33 ++++++++++++---------------------
src/backend/postmaster/bgwriter.c | 3 ---
src/backend/postmaster/checkpointer.c | 3 ---
src/backend/postmaster/postmaster.c | 17 +++++++----------
src/backend/storage/sync/sync.c | 30 +++---------------------------
src/include/storage/sync.h | 1 -
6 files changed, 22 insertions(+), 65 deletions(-)