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_17_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/fd6d3e7e9d5554bd11623d11445d82c7293e36e2
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(+)