Return valid FHIR resource as a result of $extract

[mkizesov]

Return FHIR bundle (https://www.hl7.org/fhir/bundle.html) or list (https://www.hl7.org/fhir/list.html) as a result of $extract operation.
Now it returns an array of FHIR bundles or an empty array [] (if result is empty).