only use _DMLReturningColFilter for "bulk insert", not other DML

only use _DMLReturningColFilter for "bulk insert", not other DML

Fixed bug in ORM enabled UPDATE (and theoretically DELETE) where using a
multi-table DML statement would not allow ORM mapped columns from mappers
other than the primary UPDATE mapper to be named in the RETURNING clause;
they would be omitted instead and cause a column not found exception.

Fixes: #12328
Change-Id: I2223ee506eec447823a3a545eecad1a7a03364a9