Search Parameter SearchType/DataType checking

[lmckenzi]

While validating a search parameter fhirpath expression ensire that the datatype returned by the fhirpath expression is compatible with the search type.

Reference table found in the core spec here:
https://hl7.org/fhir/search.html#table

And the code that I used in my checker is here
https://github.com/brianpos/Hl7.Fhir.FhirPath.Validator/blob/master/src/Hl7.Fhir.Base.FhirPath.Validator/SearchExpressionValidator.cs#L245

[lmckenzi]

(Moved from HL7/fhir-ig-publisher#786)

[stale]

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