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

@@ -283,7 +283,7 @@ private module AccessPaths {
 }
 
 /** Get a name of a supported generic token-based feature. */
-private string getASupportedFeatureName() {
+string getASupportedFeatureName() {
   result =
     [
       "enclosingFunctionName", "calleeName", "receiverName", "argumentIndex", "calleeApiName",
@@ -300,12 +300,5 @@ private string getASupportedFeatureName() {
 predicate tokenFeatures(DataFlow::Node endpoint, string featureName, string featureValue) {
   // Performance optimization: Restrict feature extraction to endpoints we've explicitly asked to featurize.
   endpoint = any(FeaturizationConfig cfg).getAnEndpointToFeaturize() 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

@@ -101,9 +101,9 @@ module ModelScoring {
   private int getARequestedEndpointType() { result = any(EndpointType type).getEncoding() }
 
   predicate endpointScores(DataFlow::Node endpoint, int encodedEndpointType, float score) =
-    scoreEndpoints(getARequestedEndpoint/0, getARequestedEndpointType/0,
-      EndpointFeatures::tokenFeatures/3, getACompatibleModelChecksum/0)(endpoint,
-      encodedEndpointType, score)
+    scoreEndpoints(getARequestedEndpoint/0, EndpointFeatures::tokenFeatures/3,
+      EndpointFeatures::getASupportedFeatureName/0, getARequestedEndpointType/0,
+      getACompatibleModelChecksum/0)(endpoint, encodedEndpointType, score)
 }
 
 /**