Only require "real" imports during validation of component instantiation

Currently I believe the intention for validation of instantiating a component within a component is along the lines of "iterate over all the imports and make sure something is supplied for that name and the supplied item's type is a subtype of what's required", or at least roughly that. This I think can perhaps be simplified in two ways:

• When a component imports a type with an (eq ..) bound there's not actually any need to supply that import in the object during instantiation. I would propose that a change to the validation is that if an equality-bounded type is imported then it does not need to be supplied during instantiation.

• Similarly, and perhaps as an extension of the above rule, if a component ends up importing an empty instance there's no actual need to supply such an empty instance at instantiation time. I would propose that empty instances can be omitted from the instantiation arguments.

I think that if something is supplied then it should be type-checked, but otherwise instantiation validation would allow "holes" in the supplied imports for the above cases (equality-bounded type imports and empty instances).

Start by locating the component instantiation validation logic and the tests covering imported types and instances. Confirm the intended rules in this issue: equality-bounded type imports and empty instances may be omitted, while supplied imports remain type-checked; add or update tests to demonstrate those cases.