[Bug]: TypeScript Emitter Framework shouldn't place additionalProperties on record types

This feels like an emitter-specific choice for how to represent models which extend records to me. If I want to emit an interface that represents what this looks like on the wire, I... can't?

That aside, it also presently emits just a plain record as an object type with a single property "additionalProperties" which also seems wrong - something like `tags: Record` should probably emit as `tags: { [string]: string }` or even `tags: Record` since there are no named properties to contend with.