split up psql \d Modifiers column

I propose to change the psql \d output a bit, best shown with an example:

\d persons3
- Table "public.persons3"
- Column | Type | Modifiers
---------+---------+------------------
- id | integer | not null
- name | text | default ''::text
+ Table "public.persons3"
+ Column | Type | Collation | Nullable | Default
+--------+---------+-----------+----------+----------
+ id | integer | | not null |
+ name | text | | | ''::text

The "Modifiers" column used to be "the rest", but now \d+ adds
additional columns, so throwing these three things into one column makes
less sense.

Also, some parts of that column are currently marked as translatable,
but it is not clear whether this is supposed to be an English
description or SQL text. By reducing the column contents to just the
data and moving the description to the column header, this weirdness is
avoided.

If you're worried about horizontal space, note that if a column has all
three properties, this will actually save space because the words
"collate" and "default" go away.

Patch attached. Most of it is test output changes; the code changes are
in src/bin/psql/describe.c.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services