C++: Add localExprTaint for IR

This is for ODASA-8053.

Author: jbj

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

@@ -56,6 +56,14 @@ private predicate localInstructionTaintStep(Instruction nodeFrom, Instruction no
  */
 predicate localTaint(DataFlow::Node source, DataFlow::Node sink) { localTaintStep*(source, sink) }
 
+/**
+ * Holds if taint can flow from `e1` to `e2` in zero or more
+ * local (intra-procedural) steps.
+ */
+predicate localExprTaint(Expr e1, Expr e2) {
+  localTaint(DataFlow::exprNode(e1), DataFlow::exprNode(e2))
+}
+
 /**
  * Holds if the additional step from `src` to `sink` should be included in all
  * global taint flow configurations.