R4 b fixes

[lmckenzi]

• Ensure that generated instances are compliant with the 'correct' version of the base standard - which means when we're generating R4B, we use R4 ConceptMaps and other resources, not R5. (FHIR-34433, FHIR-35783, FHIR-35784)
• Corrected FHIRtype extension values (FHIR-36036, FHIR-25275)
• Ensure that 'experimental' is set properly on canonical resources (and caseSensitive too): FHIR-34450