Refactor 'getASuccessor' to edges/3

This interface works better when defining the DFG edges in the next commit

Author: asgerf

shared/controlflow/codeql/controlflow/Cfg.qll

@@ -1324,10 +1324,10 @@ module MakeWithSplitting<
       string getOrderDisambiguation() { result = "" }
     }
 
-    Node getASuccessor(Node n, string s) {
+    predicate edge(Node node1, string label, Node node2) {
       exists(SuccessorType t |
-        result = n.getASuccessor(t) and
-        if t instanceof DirectSuccessor then s = "" else s = t.toString()
+        node2 = node1.getASuccessor(t) and
+        if t instanceof DirectSuccessor then label = "" else label = t.toString()
       )
     }
   }

shared/util/codeql/util/PrintGraph.qll

@@ -23,7 +23,7 @@ signature module InputSig<LocationSig Location> {
     string getOrderDisambiguation();
   }
 
-  Node getASuccessor(Node n, string label);
+  predicate edge(Node node1, string label, Node node2);
 }
 
 /** Provides modules for printing flow graphs. */
@@ -40,7 +40,7 @@ module PrintGraph<LocationSig Location, InputSig<Location> Input> {
   module TestOutput<RelevantNodeSig RelevantNode> {
     /** Holds if `pred -> succ` is an edge in the graph. */
     query predicate edges(RelevantNode pred, RelevantNode succ, string label) {
-      label = strictconcat(string s | succ = getASuccessor(pred, s) | s, ", " order by s)
+      label = strictconcat(string s | edge(pred, s, succ) | s, ", " order by s)
     }
 
     /**