Improve ordering for \dAo and \dAp psql commands
This commit changes ORDER BY clause for \dAo and \dAp psql commands in
the following way.
* Operators for the same types are grouped together.
* Same-class operators and procedures are listed before cross-class operators
and procedures.
Modification of ORDER BY clause for \dAp required removing DISTINCT clause,
which doesn't seem to affect anything.
Discussion: https://postgr.es/m/
20200511210856.GA18368%40alvherre.pgsql
Author: Alvaro Herrera revised by me
Reviewed-by: Alexander Korotkov, Nikita Glukhov