More strictly enforce CQFM Measure Profiles

[JPercival]

The Measure engine in this project implicitly depends on Measures largely conforming to this profile:
https://build.fhir.org/ig/HL7/cqf-measures/StructureDefinition-measure-cqfm.html

That means that things like population.id are required. We hit a number of null pointer exceptions in various test cases because we assumed that the Measure resources conformed to that profile, but in fact Measures out in the wild often do not.

We should add checks for the ids and surface more friendly error messages for Measures that are not conformant.