pgsql: Fix print of Path nodes when using OPTIMIZER_DEBUG

Fix print of Path nodes when using OPTIMIZER_DEBUG

GatherMergePath (introduced in 10) and CustomPath (introduced in 9.5)
have gone missing.  The order of the Path nodes was inconsistent with
what is listed in nodes.h, so make the order consistent at the same time
to ease future checks and additions.

Author: Sawada Masahiko
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/CAD21AoBQMLoc=ohH-oocuAPsELrmk8_EsRJjOyR8FQLZkbE0wA@mail.gmail.com

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/164ed1532f78574a904b4bd080c28105a45e2765

Modified Files
--------------
src/backend/optimizer/path/allpaths.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)