Set query ID for inner queries of CREATE TABLE AS and DECLARE

Set query ID for inner queries of CREATE TABLE AS and DECLARE

Some utility statements contain queries that can be planned and
executed: CREATE TABLE AS and DECLARE CURSOR.  This commit adds query ID
computation for the inner queries executed by these two utility
commands, with and without EXPLAIN.  This change leads to four new
callers of JumbleQuery() and post_parse_analyze_hook() so as extensions
can decide what to do with this new data.

Previously, extensions relying on the query ID, like pg_stat_statements,
were not able to track these nested queries as the query_id was 0.

For pg_stat_statements, this commit leads to additions under !toplevel
when pg_stat_statements.track is set to "all", as shown in its
regression tests.  The output of EXPLAIN for these two utilities gains a
"Query Identifier" if compute_query_id is enabled.

Author: Anthonin Bonnefoy
Reviewed-by: Michael Paquier, Jian He
Discussion: https://postgr.es/m/CAO6_XqqM6S9bQ2qd=75W+yKATwoazxSNhv5sjW06fjGAtHbTUA@mail.gmail.com