pgsql: Add further debug info to help debug 019_replslot_limit.pl failu

Add further debug info to help debug 019_replslot_limit.pl failures.

See also afdeff10526. Failures after that commit provided a few more hints,
but not yet enough to understand what's going on.

In 019_replslot_limit.pl shut down nodes with fast instead of immediate mode
if we observe the failure mode. That should tell us whether the failures we're
observing are just a timing issue under high load. PGCTLTIMEOUT should prevent
buildfarm animals from hanging endlessly.

Also adds a bit more logging to replication slot drop and ShutdownPostgres().

Discussion: /messages/by-id/20220225192941.hqnvefgdzaro6gzg@alap3.anarazel.de

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/fe0972ee5e6f8a663c5cf3f24ef98987c503da95

Modified Files
--------------
src/backend/replication/slot.c | 13 +++++++++++++
src/backend/storage/lmgr/lwlock.c | 7 +++++++
src/backend/utils/init/postinit.c | 17 +++++++++++++++++
src/include/storage/lwlock.h | 1 +
src/test/recovery/t/019_replslot_limit.pl | 18 +++++++++++++++++-
5 files changed, 55 insertions(+), 1 deletion(-)