MDEV-8789 Implement non-recursive common table expressions

[shagalla]

Initial implementation

[svoj]

Hi shagalla,

Thanks for your contribution. JIRA task just for the record: https://mariadb.atlassian.net/browse/MDEV-8789

Similar to other open source projects, the MariaDB Foundation needs to have shared ownership of all code that is included in the MariaDB distribution. The easiest way to achieve this is by submitting your code under the BSD-new license.

The other alternative is to sign the code contribution agreement which can be found here: https://mariadb.com/kb/en/mariadb/mca/

Please indicate in a comment below that you are contributing your new code of the whole pull request, including one or several files that are either new files or modified ones, under the BSD-new license or that you have filled out the contribution agreement and sent it.

Thanks,
Sergey

[svoj]

Pushed 1fc2c63