Merge pull request #247 from microsoft/add-get-callee-on-call-nodes

PS: Add `Node.getCallee` predicate on `DataFlow::CallNode`

powershell/ql/lib/semmle/code/powershell/dataflow/internal/DataFlowPublic.qll

@@ -536,6 +536,8 @@ class CallNode extends ExprNode {
    * Note that this predicate doesn't get the pipeline argument, if any.
    */
   Node getAnArgument() { result.asExpr() = call.getAnArgument() }
+
+  Node getCallee() { result.asExpr() = call.getCallee() }
 }
 
 /** A call to operator `&`, viwed as a node in a data flow graph. */