pgsql: Improve the error message for an inappropriate column definition

Improve the error message for an inappropriate column definition list.

The existing message about "a column definition list is only allowed for
functions returning "record"" could be given in some cases where it was
fairly confusing; in particular, a function with multiple OUT parameters
*does* return record according to pg_proc.  Break it down into a couple
more cases to deliver a more on-point complaint.  Per complaint from
Bruce Momjian.

Discussion: https://postgr.es/m/798909.1600562993@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/ce90f075f0d831ca4085ba73891b7da2a2f7047e

Modified Files
--------------
src/backend/parser/parse_relation.c      | 44 +++++++++++++++++++++++++++-----
src/test/regress/expected/rangefuncs.out | 13 ++++++++++
src/test/regress/sql/rangefuncs.sql      |  5 ++++
3 files changed, 55 insertions(+), 7 deletions(-)