Produce ExposedThing from a ThingModel instance

Now that a new paragraph about Thing Model is landed in the TD specification (https://github.com/w3c/wot-thing-description/pull/1024) we should evaluate possible choices about how to integrate it in the Scripting API.

As I see it, a good starting point for integrating Thing Models is in the workflow for producing ExposedThings. We could exploit the work done with ExposedThingInit and define a transformation algorithm between a TM instance and the ExposedThingInit object. We could even change the produce method signature such as it can handle ThingModel or ExposedThingInit instances as arguments.

Another option is to use the algorithm described in the mentioned PR. But as I raised during the call it is a bit vague when looking at it from an implementer's point of view. The TD group would like to keep it as it is since they would like to have a process that could be used also by tools or even humans rather than an automatic process computed by a runtime.

Opinions?

No files or tests are mentioned. Start by reading the ExposedThingInit and produce workflow, then compare the proposed ThingModel transformation with the algorithm in w3c/wot-thing-description#1024. Done means the integration choice and implementer-facing behavior are defined.