JS: Update featurization for absent features optimization

Absent features are now represented implicitly by the absence of a row
in the `tokenFeatures` relation, rather than explicitly by an empty
string. This leads to improved runtime performance. To enable this
implicit representation, we pass the set of supported token features to
the `scoreEndpoints` HOP. Requires CodeQL CLI v2.7.4.

Author: henrymercer

javascript/ql/experimental/adaptivethreatmodeling/lib/experimental/adaptivethreatmodeling/EndpointFeatures.qll

@@ -261,7 +261,7 @@ private module AccessPaths {
 }
 
 /** Get a name of a supported generic token-based feature. */
-private string getASupportedFeatureName() {
+string getASupportedFeatureName() {
   result =
     [
       "enclosingFunctionName", "calleeName", "receiverName", "argumentIndex", "calleeApiName",
@@ -277,12 +277,5 @@ private string getASupportedFeatureName() {
  */
 predicate tokenFeatures(DataFlow::Node endpoint, string featureName, string featureValue) {
   ModelScoring::endpoints(endpoint) and
-  (
-    if strictcount(getTokenFeature(endpoint, featureName)) = 1
-    then featureValue = getTokenFeature(endpoint, featureName)
-    else (
-      // Performance note: this is a Cartesian product between all endpoints and feature names.
-      featureValue = "" and featureName = getASupportedFeatureName()
-    )
-  )
+  featureValue = getTokenFeature(endpoint, featureName)
 }

javascript/ql/experimental/adaptivethreatmodeling/lib/experimental/adaptivethreatmodeling/EndpointScoring.qll

@@ -95,7 +95,8 @@ module ModelScoring {
   }
 
   predicate endpointScores(DataFlow::Node endpoint, int encodedEndpointType, float score) =
-    scoreEndpoints(endpoints/1, requestedEndpointTypes/0, relevantTokenFeatures/3,
+    scoreEndpoints(endpoints/1, relevantTokenFeatures/3,
+      EndpointFeatures::getASupportedFeatureName/0, requestedEndpointTypes/0,
       getACompatibleModelChecksum/0)(endpoint, encodedEndpointType, score)
 }