Move Evented interfaces and types from `dojo/interfaces` to `Evented.ts`

[agubler]

Enhancement

The interfaces and types related to Evented.ts should be moved from the @dojo/interfaces package into the Evented.ts module as there is little benefit to them being in a separate package. In fact it adds overhead when making changes to the Evented functionality.

[kitsonk]

Since this is ultimately a "nice to have" I have moved it to the RC, but if we can pick it up at some point ahead of that 😁

[agubler]

This will be achieved when https://github.com/dojo/meta/issues/223 is completed.

[dylans]

Resolved.