PL/SQL debugging contributions

The PL/SQL debugger incorporates work by Ziyu Yang (yangziyu1230) from:
https://github.com/yangziyu1230/dbx
Oracle: 2b4b67eb668f685c9e1972b190abccd063191060 (upstream PR #12067)
OceanBase Oracle: 1f0aed7f502997ac171e9f70f90619347ddc2767

The DBMS_DEBUG call sequences were adapted by that contribution from OceanBase
Developer Center (ODC V3.3.2.1), https://github.com/oceanbase/odc, Apache-2.0.
DBX's integration replaces the persistent helper package with anonymous system
package calls and adds shared desktop/Web session ownership and lifecycle handling.

These contributions are distributed under the Apache License, Version 2.0.
See LICENSE.