Update model info generation for US Core and QI Core to derive from FHIR

[brynrhodes]

Currently the USCore and QICore models create a flattened view of the model info and use translator mapping to compile CQL down to base FHIR. This doesn't work for all cases though; connectathon testing indicates that the mappings can't resolve without being able to be expressed in terms of FHIR, which means the USCore and QICore mappings need to derive from FHIR in order to map correctly.

This means in particular that the primary model info generation will drive off of the differential, rather than the snapshot.