Squashed commits from okeefm to support toFHIR/fromFHIR:
Squashed commits from okeefm to support toFHIR/fromFHIR:

Add mapping info for the single constraint case (but only that for the time being)

Only export non-primitive mappings

Move mapping rules block down so it's not in the middle of another concern, and add a conditional assign to ensure the mapping element is populated

Move the mapping inputs, and add a Value mapping if values are present

Actually moved code, and temporarily eliminated mappings for certain nested values

Check for undefined def.value, add mapping to the differential as well

Handle nested elements in shr mapping rule building

Modify the definition of 'no-diff' profiles, such that profiles that differ only by mapping rules are considered 'no-diff', and export the 'no-diff' profiles as a separate object

Add mappings for fields in FHIR Extensions

Change name of exported field to _noDiffProfiles

Don't apply mappings for includesTypeConstraints

standardhealth/shr-fhir-export,standardhealth/shr-fhir-export