pgsql: pg_stat_statements: Add tests for SQL/JSON query patterns

pg_stat_statements: Add tests for SQL/JSON query patterns

A new test file is added to track how the various SQL/JSON query
patterns fare in PGSS, as allowed by the parser:
- Query functions
- JSON_TABLE
- Constructors and predicates.
- etc.

This will be handy for the evaluation of some follow-up patches that aim
to tweak the query jumbling for a portion of some of these SQL/JSON
queries. Some of them are currently slightly broken, tracking as
parameters what should be a keyword, and we never knew about them.
Until now.

The author has written most of the patch. I have noticed a couple of
gaps and some inconsistencies upon further review, leading to a result
more consistent with the usual approach used by the PGSS tests.

Author: Ilya Staroverov <i(dot)staroverov(at)ftdata(dot)ru>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/457969A9-5D24-422F-B09E-F388053DE028@localhost.localdomain

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ae75d12b500f01eb3ce9a46418beb2e9301e3e0b

Modified Files
--------------
contrib/pg_stat_statements/Makefile | 1 +
contrib/pg_stat_statements/expected/sqljson.out | 1369 +++++++++++++++++++++++
contrib/pg_stat_statements/meson.build | 1 +
contrib/pg_stat_statements/sql/sqljson.sql | 391 +++++++
4 files changed, 1762 insertions(+)