pgsql: Move any code specific to log_destination=csvlog to its own file

Move any code specific to log_destination=csvlog to its own file

The recent refactoring done in ac7c807 makes this move possible and
simple, as this just moves some code around.  This reduces the size of
elog.c by 7%.

Author: Michael Paquier, Sehrope Sarkuni
Reviewed-by: Nathan Bossart
Discussion: https://postgr.es/m/CAH7T-aqswBM6JWe4pDehi1uOiufqe06DJWaU5=X7dDLyqUExHg@mail.gmail.com

simply moves the routines related to csvlog into their own file

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bed6ed3de9b3e62d8c6ee034513d04d769091927

Modified Files
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src/backend/utils/error/Makefile |   1 +
src/backend/utils/error/csvlog.c | 264 +++++++++++++++++++++++++++++++++++++++
src/backend/utils/error/elog.c   | 231 ----------------------------------
3 files changed, 265 insertions(+), 231 deletions(-)