Data flow: Allow nodes to be hidden from path explanations

cpp/ql/src/semmle/code/cpp/dataflow/internal/DataFlowPrivate.qll

@@ -314,3 +314,6 @@ predicate isImmutableOrUnobservable(Node n) {
   // The above list of cases isn't exhaustive, but it narrows down the
   // consistency alerts enough that most of them are interesting.
 }
+
+/** Holds if `n` should be hidden from path explanations. */
+predicate nodeIsHidden(Node n) { none() }

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll

@@ -306,3 +306,6 @@ predicate isImmutableOrUnobservable(Node n) {
   // complex to model here.
   any()
 }
+
+/** Holds if `n` should be hidden from path explanations. */
+predicate nodeIsHidden(Node n) { none() }