JavaScript: Introduce DataFlow::ExprNode and exprNode for consistency with other languages.

javascript/ql/src/semmle/javascript/dataflow/DataFlow.qll

@@ -980,6 +980,11 @@ module DataFlow {
    */
   ValueNode valueNode(ASTNode nd) { result.getAstNode() = nd }
 
+  /**
+   * Gets the data flow node corresponding to `e`.
+   */
+  ExprNode exprNode(Expr e) { result = valueNode(e) }
+
   /** Gets the data flow node corresponding to `ssa`. */
   SsaDefinitionNode ssaDefinitionNode(SsaDefinition ssa) { result = TSsaDefNode(ssa) }
 

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

@@ -6,6 +6,11 @@
 
 import javascript
 
+/** A data flow node corresponding to an expression. */
+class ExprNode extends DataFlow::ValueNode {
+  override Expr astNode;
+}
+
 /** A data flow node corresponding to a parameter. */
 class ParameterNode extends DataFlow::SourceNode {
   Parameter p;