YSQL transactional DDL support enables yb.port.rowsecurity test

The YugaByte/yugabyte-db release 2026.1.2.0-b87 re-enables the yb.port.rowsecurity regression test for YSQL, according to the project's GitHub release notes. This change follows the introduction of support for interleaving SAVEPOINT with DDL inside a transaction block, which was previously unsupported. The test now passes with the preview flag ysql_yb_enable_ddl_savepoint_support enabled, which impacts the entire yb_pg_auth_schedule test suite. Additionally, four cleanup statements previously used as workarounds for the lack of transactional DDL have been removed, as transactional DDL now ensures proper rollback behavior. Updates to expected outputs address changes in query plans and aliasing introduced by earlier commits.

Operators should verify whether their workloads depend on the preview flag ysql_yb_enable_ddl_savepoint_support, as its activation affects broader test schedules beyond yb.port.rowsecurity. Additionally, any reliance on cleanup statements or specific aliasing in query plans should be reviewed, as these behaviors may differ after upgrading. This pattern of enabling previously unsupported features highlights the importance of testing transactional DDL interactions in complex environments before deployment.