pgsql: Improve ordering for \dAo and \dAp psql commands

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

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/b1953e67e4c481f8d3844dcdd8fdd4054d7e7604

Modified Files
--------------
src/bin/psql/describe.c | 13 ++++++---
src/test/regress/expected/psql.out | 57 +++++++++++++++++++++++++-------------
src/test/regress/sql/psql.sql | 4 +--
3 files changed, 49 insertions(+), 25 deletions(-)