pgsql: Preserve the owner of extended statistics rebuilt by ALTER TABLE

Preserve the owner of extended statistics rebuilt by ALTER TABLE.

When ALTER TABLE ... ALTER COLUMN TYPE (or any subcommand that rebuilds
them) drops and re-creates the extended statistics objects depending on
the altered column, the re-created objects were owned by the role running
ALTER TABLE rather than by the original owner of the statistics.

Remember each object's owner before dropping it, and restore it on
re-creation.

CreateStatistics()'s signature changes and CreateStatsStmt gains a field,
but no known third-party code calls the former or constructs the latter.

Author: Masahiko Sawada 
Reviewed-by: Noah Misch 
Backpatch-through: 14
Security: CVE-2026-6469

Branch
------
REL_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/fb6d1ca8d746dc1ca0e32890a50d7b93d2fbebae
Author: Masahiko Sawada 

Modified Files
--------------
src/backend/commands/statscmds.c        | 48 ++++++++++++++----------------
src/backend/commands/tablecmds.c        | 52 ++++++++++++++++++++++++---------
src/backend/tcop/utility.c              | 19 ++++++++++--
src/include/commands/defrem.h           |  2 +-
src/include/nodes/parsenodes.h          |  1 +
src/test/regress/expected/stats_ext.out | 29 ++++++++++++++++++
src/test/regress/sql/stats_ext.sql      | 20 +++++++++++++
7 files changed, 129 insertions(+), 42 deletions(-)