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

Branch
------
REL_13_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/8a2530ebcdef1aafa08ad1d019aec298dcebb952

Modified Files
--------------
src/backend/commands/statscmds.c | 8 ++++++++
src/test/regress/expected/stats_ext.out | 14 ++++++++++++++
src/test/regress/sql/stats_ext.sql | 13 +++++++++++++
3 files changed, 35 insertions(+)