pgsql: Move pg_stat_statements query jumbling to core.

Move pg_stat_statements query jumbling to core.

Add compute_query_id GUC to control whether a query identifier should be
computed by the core (off by default). It's thefore now possible to
disable core queryid computation and use pg_stat_statements with a
different algorithm to compute the query identifier by using a
third-party module.

To ensure that a single source of query identifier can be used and is
well defined, modules that calculate a query identifier should throw an
error if compute_query_id specified to compute a query id and if a query
idenfitier was already calculated.

Discussion: https://postgr.es/m/20210407125726.tkvjdbw76hxnpwfi@nol

Author: Julien Rouhaud

Reviewed-by: Alvaro Herrera, Nitin Jadhav, Zhihong Yu

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/5fd9dfa5f50e4906c35133a414ebec5b6d518493

Modified Files
--------------
contrib/pg_stat_statements/pg_stat_statements.c | 805 +-------------------
contrib/pg_stat_statements/pg_stat_statements.conf | 1 +
doc/src/sgml/config.sgml | 25 +
doc/src/sgml/pgstatstatements.sgml | 20 +-
src/backend/parser/analyze.c | 14 +-
src/backend/tcop/postgres.c | 6 +-
src/backend/utils/misc/Makefile | 1 +
src/backend/utils/misc/guc.c | 10 +
src/backend/utils/misc/postgresql.conf.sample | 1 +
src/backend/utils/misc/queryjumble.c | 834 +++++++++++++++++++++
src/include/parser/analyze.h | 4 +-
src/include/utils/guc.h | 1 +
src/include/utils/queryjumble.h | 58 ++
13 files changed, 995 insertions(+), 785 deletions(-)