Dataflow: Address review comments.

Author: aschackmull

shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll

@@ -2486,6 +2486,11 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
           callEdgeReturn(call, c, _, _, _, _, _)
         }
 
+        /**
+         * INTERNAL: Only for debugging.
+         *
+         * Provides a graph representation of the data flow in this stage suitable for use in a `path-problem` query.
+         */
         additional module Graph {
           private newtype TStagePathNode =
             TStagePathNodeMid(
@@ -2503,6 +2508,9 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
 
             abstract Location getLocation();
 
+            /** Gets the corresponding `Node`, if any. */
+            Node getNode() { none() }
+
             predicate isSource() { none() }
 
             predicate isSink() { none() }
@@ -2545,6 +2553,8 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
 
             override Location getLocation() { result = node.getLocation() }
 
+            override Node getNode() { result = node.asNode() }
+
             override predicate isSource() {
               sourceNode(node, state) and
               (if hasSourceCallCtx() then cc = ccSomeCall() else cc = ccNone()) and