pgsql: Add backend-level lock statistics

Add backend-level lock statistics

This commit adds per-backend lock statistics, providing the same
information as pg_stat_lock. It is now possible to retrieve those stats
(lock wait counts, wait times, and fast-path exceeded count) on a
per-backend basis.

This data can be retrieved with a new system function called
pg_stat_get_backend_lock(), that returns one tuple per lock type based
on the PID provided in input. Like pg_stat_get_backend_io(), this is
useful if joined with pg_stat_activity to get a live picture of the
locks behavior for each running backend.

pgstat_flush_backend() gains a new flag value, able to control the flush
of the lock stats.

This commit is straight-forward, relying on the infrastructure provided
by 9aea73fc61d4 (backend-level pgstats).

Bump catalog version. No need to touch PGSTAT_FILE_FORMAT_ID as backend
statistics are never written to disk.

Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Reviewed-by: Tatsuya Kawata <kawatatatsuya0913(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Tristan Partin <tristan(at)partin(dot)io>
Reviewed-by: Rui Zhao <zhaorui126(at)gmail(dot)com>
Discussion: https://postgr.es/m/aiAzEY+cMQb/W8yu(at)bdtpg

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/8c579bdc366dbca4fe9432a01408216133628c52

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 19 ++++++++
src/backend/utils/activity/pgstat_backend.c | 72 +++++++++++++++++++++++++++++
src/backend/utils/activity/pgstat_lock.c | 4 ++
src/backend/utils/adt/pgstatfuncs.c | 29 +++++++++++-
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 8 ++++
src/include/pgstat.h | 12 +++++
src/include/utils/pgstat_internal.h | 3 +-
src/test/regress/expected/stats.out | 12 +++++
src/test/regress/sql/stats.sql | 9 ++++
10 files changed, 166 insertions(+), 4 deletions(-)