Make auto_explain print the query identifier in verbose mode

Make auto_explain print the query identifier in verbose mode

When auto_explain.log_verbose is on, auto_explain should print in the
logs plans equivalent to the EXPLAIN (VERBOSE).  However, when
compute_query_id is on, query identifiers were not showing up, being
only handled by EXPLAIN (VERBOSE).  This brings auto_explain on par with
EXPLAIN regarding that.  Note that like EXPLAIN, auto_explain does not
show the query identifier when compute_query_id=regress.

The change is done so as the choice of printing the query identifier is
done in ExplainPrintPlan() rather than in ExplainOnePlan(), to avoid a
duplication of the logic dealing with the query ID.  auto_explain is the
only in-core caller of ExplainPrintPlan().

While looking at the area, I have noticed that more consolidation
between EXPLAIN and auto_explain would be in order for the logging of
the plan duration and the buffer usage.  This refactoring is left as a
future change.

Author: Atsushi Torikoshi
Reviewed-by: Justin Pryzby, Julien Rouhaud
Discussion: https://postgr.es/m/1ea21936981f161bccfce05765c03bee@oss.nttdata.com