Implement Id SearchParameter for InMemoryRepository

[JPercival]

The InMemoryRepository located here indexes resources by Id, but does not take advantage of that when an _id parameter is passed. Instead, it scans through the list of resources and uses the ResourceMatcher to do the matching.

https://github.com/cqframework/clinical-reasoning/blob/master/cqf-fhir-utility/src/main/java/org/opencds/cqf/fhir/utility/repository/InMemoryFhirRepository.java

We should change this to first look-up by Id if requested, and then apply any additional filters.

Sample CQL:

[Condition : id in {`123`}]

Acceptance criteria:

• _id parameter support is added to InMemoryRepository
• Tests added to validate that behavior

[JPercival]

Resolved by #353