use _generate_columns_plus_names for ddl returning c populate

use _generate_columns_plus_names for ddl returning c populate

Improved the implementation of :meth:`.UpdateBase.returning` to use more
robust logic in setting up the ``.c`` collection of a derived statement
such as a CTE.  This fixes issues related to RETURNING clauses that feature
expressions based on returned columns with or without qualifying labels.

Co-authored-by: Juhyeong Ko <dury.ko@gmail.com>
Fixes: #12271
Change-Id: Id0d486d4304002f1affdec2e7662ac2965936f2a
(cherry picked from commit 4c4011b50bf8f2f6acca86b11ae3d900b30034a0)