Ensure TypeDecorator delegates _set_parent_with_dispatch as well as
_set_parent to itself as well as its impl, as the TypeDecorator
class itself may have an active SchemaType implementation as well.
Fixed regression which occurred as a side effect of 🎫`2919`,
which in the less typical case of a user-defined
:class:`.TypeDecorator` that was also itself an instance of
:class:`.SchemaType` (rather than the implementation being such)
would cause the column attachment events to be skipped for the
type itself.
Change-Id: I0afb498fd91ab7d948e4439e7323a89eafcce0bc
Fixes: #3832
Mike Bayer
30bd28fca2