pgsql: Check for CREATE privilege on the schema in CREATE STATISTICS.

Check for CREATE privilege on the schema in CREATE STATISTICS.

This omission allowed table owners to create statistics in any
schema, potentially leading to unexpected naming conflicts.  For
ALTER TABLE commands that require re-creating statistics objects,
skip this check in case the user has since lost CREATE on the
schema.  The addition of a second parameter to CreateStatistics()
breaks ABI compatibility, but we are unaware of any impacted
third-party code.

Reported-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Co-authored-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Security: CVE-2025-12817
Backpatch-through: 13

Branch
------
REL_17_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/e2fb3dfa817fbe89494a62c100e9cb442f4d6b15

Modified Files
--------------
src/backend/commands/statscmds.c        | 17 ++++++++++++++-
src/backend/commands/tablecmds.c        |  2 +-
src/backend/tcop/utility.c              |  2 +-
src/include/commands/defrem.h           |  2 +-
src/test/regress/expected/stats_ext.out | 37 +++++++++++++++++++++++++++++++++
src/test/regress/sql/stats_ext.sql      | 34 ++++++++++++++++++++++++++++++
6 files changed, 90 insertions(+), 4 deletions(-)