- The :class:`.TypeDecorator` type extender will now work in conjunction

- The :class:`.TypeDecorator` type extender will now work in conjunction
with a :class:`.SchemaType` implementation, typically :class:`.Enum`
or :class:`.Boolean` with regards to ensuring that the per-table
events are propagated from the implementation type to the outer type.
These events are used
to ensure that the constraints or Postgresql types (e.g. ENUM)
are correctly created (and possibly dropped) along with the parent
table.
fixes #2919