match ORM mapped cols to PK in interpret_returning_rows

match ORM mapped cols to PK in interpret_returning_rows

Fixed bug in ORM "update with WHERE clause" feature where an explicit
``.returning()`` would interfere with the "fetch" synchronize strategy due
to an assumption that the ORM mapped class featured the primary key columns
in a specific position within the RETURNING.  This has been fixed to use
appropriate ORM column targeting.

the _interpret_returning_rows method looked to be mostly not used as far
as its joined inheritance features, which appear to have never been
used as joined inheritance mappers are skipped.

Fixes: #11997
Change-Id: I38fe3a84cdeb2eef38fe00d8b9a6a2b56f434bc6