Ruby: Add getPositionalArgument

This gets positional arguments from a call. These are arguments which
are not keyword arguments.

ruby/ql/lib/codeql/ruby/controlflow/CfgNodes.qll

@@ -357,6 +357,14 @@ module ExprNodes {
       )
     }
 
+    /**
+     * Gets the `nth` positional argument of this call.
+     * Unlike `getArgument`, this excludes keyword arguments.
+     */
+    final ExprCfgNode getPositionalArgument(int n) {
+      result = this.getArgument(n) and not result instanceof PairCfgNode
+    }
+
     /** Gets the number of arguments of this call. */
     final int getNumberOfArguments() { result = e.getNumberOfArguments() }
 

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPublic.qll

@@ -71,6 +71,14 @@ class CallNode extends LocalSourceNode, ExprNode {
   /** Gets the data-flow node corresponding to the named argument of the call corresponding to this data-flow node */
   ExprNode getKeywordArgument(string name) { result.getExprNode() = node.getKeywordArgument(name) }
 
+  /**
+   * Gets the `nth` positional argument of this call.
+   * Unlike `getArgument`, this excludes keyword arguments.
+   */
+  final ExprNode getPositionalArgument(int n) {
+    result.getExprNode() = node.getPositionalArgument(n)
+  }
+
   /** Gets the name of the the method called by the method call (if any) corresponding to this data-flow node */
   string getMethodName() { result = node.getExpr().(MethodCall).getMethodName() }