Use a cached context for increased performance. The default construct…

…or R4FhirModelResolver() constructor recreates the FhirContext. (#1753)

workflow/src/main/java/com/google/android/fhir/workflow/FhirOperator.kt

@@ -56,6 +56,11 @@ import org.opencds.cqf.cql.evaluator.measure.r4.R4MeasureProcessor
 import org.opencds.cqf.cql.evaluator.plandefinition.OperationParametersParser
 import org.opencds.cqf.cql.evaluator.plandefinition.r4.PlanDefinitionProcessor
 
+// Uses the already cached FhirContext instead of creating a new one
+// on the default protected R4FhirModelResolver() constructor.
+// This is a heavy object to load. Avoid having to create a new one.
+object cachedR4FhirModelResolver : R4FhirModelResolver(FhirContext.forR4Cached())
+
 class FhirOperator(fhirContext: FhirContext, fhirEngine: FhirEngine) {
  // Initialize the measure processor
  private val fhirEngineTerminologyProvider = FhirEngineTerminologyProvider(fhirContext, fhirEngine)
@@ -69,7 +74,7 @@ class FhirOperator(fhirContext: FhirContext, fhirEngine: FhirEngine) {
  }
  private val dataProvider =
  CompositeDataProvider(
- CachingModelResolverDecorator(R4FhirModelResolver()),
+ CachingModelResolverDecorator(cachedR4FhirModelResolver),
  fhirEngineRetrieveProvider
  )
  private val fhirEngineDal = FhirEngineDal(fhirEngine)