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_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/2e91f8548daa7c7c7d5848f3812fac95fe9e9db5
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(+)