pgsql: Provide log_status_format(), useful for an emit_log_hook.

Provide log_status_format(), useful for an emit_log_hook.

Refactor so that log_line_prefix() is a thin wrapper over a new
function log_status_format(), and move the implementation to the
latter. Export log_status_format() so that it can be used by an
emit_log_hook.

Discussion: https://postgr.es/m/39c8197652f4d3050aedafae79fa5af31096505f.camel%40j-davis.com
Reviewed-by: Michael Paquier, Alvaro Herrera

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b40baa96a7ad789718dcf59b1dd73bae15c3a7e1

Modified Files
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src/backend/utils/error/elog.c | 15 ++++++++++++---
src/include/utils/elog.h       |  4 ++++
2 files changed, 16 insertions(+), 3 deletions(-)