JS: Move VarAccessBarrier outside the deprecated Configuration.qll file

javascript/ql/lib/semmle/javascript/dataflow/Nodes.qll

@@ -1708,3 +1708,18 @@ class RegExpCreationNode extends DataFlow::SourceNode {
     result = this.getAReference(DataFlow::TypeTracker::end())
   }
 }
+
+/**
+ * A guard node for a variable in a negative condition, such as `x` in `if(!x)`.
+ * Can be added to a `isBarrier` in a data-flow configuration to block flow through such checks.
+ */
+class VarAccessBarrier extends DataFlow::Node {
+  VarAccessBarrier() {
+    exists(ConditionGuardNode guard, SsaRefinementNode refinement |
+      this = DataFlow::ssaDefinitionNode(refinement) and
+      refinement.getGuard() = guard and
+      guard.getTest() instanceof VarAccess and
+      guard.getOutcome() = false
+    )
+  }
+}