add variant render step for user-defined types

add variant render step for user-defined types

due to SQLA 2.0's variant being integrated into types,
the variant rendering conditional would no longer take effect
as the type was not under the "sqlalchemy" module namespace.

Fixed issue where rendering of user-defined types that then went onto use
the ``.with_variant()`` method would fail to render, if using SQLAlchemy
2.0's version of variants.

Change-Id: I3c6f14325d6dffb2ddc1bf955753ee5a2de2cedd
Fixes: #1167