days between DateTime with Uncertain Interval returns string instead of interval

[bryantaustin13]

days between DateTime(2014, 1, 15) and DateTime(2014, 2) when evaluated returns a String, “Interval[16, 44]“, not an Interval object

To duplicate the error run this test against cql-tests-runner:

<?xml version="1.0" encoding="utf-8"?>
<tests xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://hl7.org/fhirpath/tests" xsi:schemaLocation="http://hl7.org/fhirpath/tests ../../testSchema/testSchema.xsd"
	   name="CqlIntervalOperatorsTest" reference="https://cql.hl7.org/09-b-cqlreference.html#interval-operators-3" version="1.0">
	<group name="IntervalFail" version="1.0">
		<test name="DateTimeDurationBetweenUncertainInterval" version="1.4">
			<capability code="precision-based-timing"/>
			<capability code="uncertainty-intervals"/>
			<expression>days between DateTime(2014, 1, 15) and DateTime(2014, 2)</expression>
			<output>Interval[ 16, 44 ]</output>
		</test>
	</group>
</tests>

A number of cql-tests in the CqlIntervalOperators file depend on this. Currently showing an error because it is expecting an object not a string.

[bryantaustin13]

moved to clinical_quality_language #1724