Investigate and fix errors in our sources that lead to fatal errors in the validator

[Kasdejong]

• When creating a resolver for the context of a test, we are still using the old parsers in the underlying model. Or, in an case, we are running the TypedElementOnSourceNode type checks on the profiles instead of working with partial results. (Encountered an error while loading schema 'http://hl7.org.au/fhir/StructureDefinition/au-patient': Type checking the data: Encountered unknown element 'xpath' at location 'StructureDefinition.snapshot[0].element[0].constraint[0].xpath[0])
• When a schema cannot be resolved by the underlying sources, we throw -1 ("Encountered an error while loading schema 'http://phr.kanta.fi/StructureDefinition/fiphr-pef-stu3': Compiler needs access to profile 'http://phr.kanta.fi/StructureDefinition/fiphr-patient-stu3', but it cannot be resolved.")
• we seem to be doing something wrong with versioning here, or we just do not support this. This happens for all versioned references like these. "Encountered an error while loading schema 'http://hl7.org/fhir/us/mcode/StructureDefinition/mcode-cancer-genetic-variant': File was not found: 'hl7.fhir.us.core#3.1.0'."

[alexzautke]

See also #551 for subissue nr. 2