Add support for validating multiple resources together.

[ElliotSilver]

We would like to validate a collection of individual resources (incidentally the example resources from an IG), however some profile constraints span multiple resources. For example, profiles that require reference targets to meet certain types or profiles, or slicing discriminators that depend on values in reference targets. In these cases, it would be helpful to validate a collection of resources together.

I imagine that the validator could have an option so that all resources passed in are used to establish the context of each other, or that an (imaginary) Bundle is wrapped around all the resources and the Bundle is validated. This wouldn't change that the resources are validated against an IG, etc. In some ways, this is the opposite of the existing "assumeValidRestReferences"

See https://chat.fhir.org/#narrow/stream/179252-IG-creation/topic/Validating.20other.20packages/near/404170997

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 5 days if no further activity occurs. Thank you for your contributions.