[Quest] - Support for all FHIR nested models in StructureMap-based extraction and documentation of the names

[ekigamba]

Name of feature to enhance Support for all FHIR nested models in StructureMap-based extraction

Description of feature

StructureMap-based extraction enables you to easily create new instances of models using create("ModelName")

Describe the enhancement Currently, we are not able to create instances of FHIR nested models eg. Group.GroupCharacteristicComponent and have to manually add support in the TransformSupportServices class.

The solution is either to:

• Figure out if running the extraction with the NPM package solves the issue
• Write code generation for all the nested models using the NPM package as the source

This will require discussions with the FHIR community to understand whether this is missing functionality and if so, if this should be implemented on FHIR Core, Android FHIR SDK or the implementing partners codebase. We optionally need documentation for the names to use when authoring StructureMaps because the FHIR documentation only terms them as BackboneElement while the JSON schema model from the NPM package has the specific name of the nested model

[ekigamba]

Here is the NPM Package https://drive.google.com/file/d/124sAt91B0PiY075HiTgw3U6pxp2eSUTT/view?usp=sharing that we previously removed from the codebase in this PR https://github.com/google/android-fhir/pull/844