Profile the performance of the Luhn calculation in FhirPath

[ewoutkramer]

US Core Organization now contains a FHIRPath statement that does a Luhn check on an Identifier, see us-core-17 here:
https://www.hl7.org/fhir/us/core/StructureDefinition-us-core-organization.html

This historically triggered a deficiency in the FhirPath evaluator and used to be very slow. We might have solved that (or are going to solve that using #2720 ) - but we need to check whether we do a better job now, before this profile becomes popular.

[brianpos]

This is also in the HL7 Australia identifiers too.