fix(fhir): make sure fields configured via _summary are...

...returned even if user explicitly specifies additional fields via
`_elements`

Author: cmark

core/com.b2international.snowowl.core/src/com/b2international/snowowl/core/request/IndexResourceRequestBuilder.java

@@ -34,6 +34,10 @@ public abstract class IndexResourceRequestBuilder<B extends IndexResourceRequest
 
 	protected IndexResourceRequestBuilder() {}
 
+	protected final List<String> fields() {
+		return fields;
+	}
+	
 	public final B setExpand(String...expand) {
 		if (!CompareUtils.isEmpty(expand)) {
 			return setExpand(String.join(",", expand));

fhir/com.b2international.snowowl.fhir.core/src/com/b2international/snowowl/fhir/core/request/FhirResourceSearchRequestBuilder.java

@@ -106,7 +106,7 @@ public final B setElements(Iterable<String> elements) {
 		if (elements == null) {
 			return getSelf();
 		} else {
-			final Set<String> fields = new LinkedHashSet<>();
+			final Set<String> fields = new LinkedHashSet<>(fields()); // always get the already configured field values 
 			// when called with a non-null value, make sure mandatory fields are implicitly included
 			fields.addAll(getMandatoryFields());
 			// add all other fields