support memberOf check against new CodeableReference datatype

[lmsurpre]

Is your feature request related to a problem? Please describe.
In the current r4b-rebased branch, one of our ClinicalUseDefinition examples fails validation due to the following:

Caused by: java.lang.RuntimeException: An error occurred while validating constraint: clinicalUseDefinition-5 with location: indication.intendedEffect and expression: $this.memberOf('http://hl7.org/fhir/ValueSet/product-intended-use', 'preferred') at path: ClinicalUseDefinition
	at com.ibm.fhir.validation.FHIRValidator$ValidatingNodeVisitor.validate(FHIRValidator.java:436)
	at com.ibm.fhir.validation.FHIRValidator$ValidatingNodeVisitor.validate(FHIRValidator.java:368)
	at com.ibm.fhir.validation.FHIRValidator$ValidatingNodeVisitor.validate(FHIRValidator.java:337)
	at com.ibm.fhir.validation.FHIRValidator$ValidatingNodeVisitor.doVisit(FHIRValidator.java:297)
	at com.ibm.fhir.path.visitor.FHIRPathDefaultNodeVisitor.visit(FHIRPathDefaultNodeVisitor.java:81)
	at com.ibm.fhir.path.FHIRPathResourceNode.accept(FHIRPathResourceNode.java:197)
	at com.ibm.fhir.validation.FHIRValidator$ValidatingNodeVisitor.validate(FHIRValidator.java:269)
	at com.ibm.fhir.validation.FHIRValidator.validate(FHIRValidator.java:217)
	... 36 more
Caused by: com.ibm.fhir.path.exception.FHIRPathException: java.lang.IllegalArgumentException: The 'memberOf' function must be invoked on a coded element node, quantity element node, string element node, or uri element node  [probeId=7f-0-0-1-427f7dfa-6586-4683-a347-a9e1266e3bb0]
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator.evaluate(FHIRPathEvaluator.java:257)
	at com.ibm.fhir.validation.FHIRValidator$ValidatingNodeVisitor.validate(FHIRValidator.java:414)
	... 43 more
Caused by: java.lang.IllegalArgumentException: The 'memberOf' function must be invoked on a coded element node, quantity element node, string element node, or uri element node
	at com.ibm.fhir.path.function.MemberOfFunction.apply(MemberOfFunction.java:88)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator$EvaluatingVisitor.visitFunction(FHIRPathEvaluator.java:1200)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator$EvaluatingVisitor.visitFunction(FHIRPathEvaluator.java:1)
	at com.ibm.fhir.path.FHIRPathParser$FunctionContext.accept(FHIRPathParser.java:1140)
	at org.antlr.v4.runtime.tree.AbstractParseTreeVisitor.visitChildren(AbstractParseTreeVisitor.java:46)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator$EvaluatingVisitor.visitFunctionInvocation(FHIRPathEvaluator.java:1124)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator$EvaluatingVisitor.visitFunctionInvocation(FHIRPathEvaluator.java:1)
	at com.ibm.fhir.path.FHIRPathParser$FunctionInvocationContext.accept(FHIRPathParser.java:1051)
	at org.antlr.v4.runtime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.java:18)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator$EvaluatingVisitor.visitInvocationExpression(FHIRPathEvaluator.java:863)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator$EvaluatingVisitor.visitInvocationExpression(FHIRPathEvaluator.java:1)
	at com.ibm.fhir.path.FHIRPathParser$InvocationExpressionContext.accept(FHIRPathParser.java:279)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator$EvaluatingVisitor.evaluate(FHIRPathEvaluator.java:302)
	at com.ibm.fhir.path.evaluator.FHIRPathEvaluator.evaluate(FHIRPathEvaluator.java:255)
	... 44 more

I think its because this indication.intendedEffect is of type "CodeableReference"

Describe the solution you'd like
Allow memberOf to execute against FHIR elements with this new data type.

Describe alternatives you've considered

Acceptance Criteria

1. validation should work against instances that use this new datatype like ClinicalUseDefinition

Additional context

[punktilious]

Check we can CREATE all the ClinicalUseDefinition resources in our examples:

for file in $(find /path/to/git/FHIR/fhir-examples -name 'ClinicalUseDefinition*.json'); do
    curl -k -i \
    -H 'Content-Type: application/json' \
    -X POST \
    -u 'fhiruser:change-password' 'https://localhost:9443/fhir-server/api/v4/ClinicalUseDefinition' \
    -d "@${file}"
done

Every example gets a 201 response.

[punktilious]

Note search parameters do not currently work for the CodeableReference datatype. See #3854