Force testing of query jumbling code in TAP tests

Hi all,

As mentioned two times on this thread, there is not much coverage for
the query jumbling code, even if it is in core:
https://www.postgresql.org/message-id/Y5BHOUhX3zTH/ig6(at)paquier(dot)xyz

Ths issue is that we have the options to enable it, but only
pg_stat_statements is able to enable and stress it. This causes
coverage to be missed for all query patterns that are not covered
directly by pg_stat_statements, like XML expressions, various DML
patterns, etc. More aggressive testing would also ensure that no
nodes are marked as no_query_jumble while they should be included in a
computation.

Attached is a patch to improve that. The main regression database is
able to cover everything, basically, so I'd like to propose the
addition of some extra configuration in 027_stream_regress.pl to
enable pg_stat_statements. This could be added in the pg_upgrade
tests, but that felt a bit less adapted here. Or can people think
about cases where checking pg_stat_statements makes more sense after
an upgrade or on a standby? One thing that makes sense for a standby
is to check that the contents of pg_stat_statements are empty?

With this addition, the query jumbling gets covered at 95%~, while
https://coverage.postgresql.org/src/backend/nodes/index.html reports
currently 35%.

Thoughts or comments?
--
Michael