Allow specialized validation and editing of component objects in non-OpenAPI files

[tedepstein]

Extracted from #488.

Provide a way to edit objects of a recognized component type (e.g. schema, parameter, response, etc.) in YAML files that do not conform to OpenAPI. Specifically:

• Since the file is not an OpenAPI document, don't attempt to validate the entire document as such.
• Since an object within that file is recognized as one of the referencable component types defined in OpenAPI, or is being referenced (directly or indirectly) from a valid OpenAPI file, allow specialized editing with code assist and validation on that object.

[tedepstein]

Note: I won't try to elaborate on possible design considerations for a feature like this. I'll just say that the idea, even using a minimal design in a tightly bounded set of cases, is very difficult!