Prefer getId() as data source API for getting string-based ids

The CQL execution engine requires that data models expose an id over the
API and it expects that this id is a string.  Currently this is only
used when building out the results object (in which the patient id is
used as a key) -- but it is important.

Problems arise when a data model defines an id property that is not a
string.  This is the case for the FHIR data models (in which id is an
object, in order to support extensions).  Then the required string-based
id conflicts with the data-model defined object id.

To get around this, we change the API to expect a getId() function that
should return the ID as a string.  To support backwards compatibility
(i.e., not break Bonnie and other apps), if the getId() function isn't
found, we fall back to id().

src/example/browser/cql4browsers.js

@@ -43831,8 +43831,9 @@
     }
 
     Results.prototype.recordPatientResult = function(patient_ctx, resultName, result) {
-      var base, patientId;
-      patientId = patient_ctx.patient.id();
+      var base, p, patientId;
+      p = patient_ctx.patient;
+      patientId = typeof p.getId === 'function' ? p.getId() : p.id();
       if ((base = this.patientResults)[patientId] == null) {
         base[patientId] = {};
       }

src/runtime/results.coffee

@@ -5,7 +5,11 @@ module.exports.Results = class Results
     @localIdPatientResultsMap = {}
 
   recordPatientResult: (patient_ctx, resultName, result) ->
-    patientId = patient_ctx.patient.id()
+    p = patient_ctx.patient
+    # NOTE: From now on prefer getId() over id() because some data models may have an id property
+    # that is not a string (e.g., FHIR) -- so reserve getId() for the API (and expect a string
+    # representation) but leave id() for data-model specific formats.
+    patientId = if typeof p.getId == 'function' then p.getId() else p.id()
     @patientResults[patientId] ?= {}
     @patientResults[patientId][resultName] = result
     @localIdPatientResultsMap[patientId] = patient_ctx.getAllLocalIds()