pgsql: Check for USAGE privilege on the subtype in CREATE TYPE AS RANGE

Check for USAGE privilege on the subtype in CREATE TYPE AS RANGE.

This omission allowed roles without USAGE on a type to create range
types that depend on it, which could prevent the owner from
changing the type later.

Reported-by: Jingzhou Fu <fuboat(at)outlook(dot)com>
Author: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Reviewed-by: Noah Misch <noah(at)leadboat(dot)com>
Reviewed-by: Robert Haas <robertmhaas(at)gmail(dot)com>
Security: CVE-2026-6470
Backpatch-through: 14

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/efdb260728c93f605f9ef7aaef56b013f6bb87b7
Author: Nathan Bossart <nathan(at)postgresql(dot)org>

Modified Files
--------------
doc/src/sgml/ref/create_type.sgml | 5 +++++
src/backend/commands/typecmds.c | 4 ++++
src/test/regress/expected/rangetypes.out | 15 +++++++++++++++
src/test/regress/sql/rangetypes.sql | 14 ++++++++++++++
4 files changed, 38 insertions(+)