Merge pull request github#11126 from hvitved/cpp/position-overrides

C++: Let `(Indirect|Direct)Position` be sub classes of `Position`

Author: hvitved

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll

@@ -98,16 +98,16 @@ class ParameterPosition = Position;
 /** An argument position represented by an integer. */
 class ArgumentPosition = Position;
 
-class Position extends TPosition {
+abstract class Position extends TPosition {
   abstract string toString();
 }
 
-class DirectPosition extends TDirectPosition {
+class DirectPosition extends Position, TDirectPosition {
   int index;
 
   DirectPosition() { this = TDirectPosition(index) }
 
-  string toString() {
+  override string toString() {
     index = -1 and
     result = "this"
     or
@@ -118,12 +118,12 @@ class DirectPosition extends TDirectPosition {
   int getIndex() { result = index }
 }
 
-class IndirectionPosition extends TIndirectionPosition {
+class IndirectionPosition extends Position, TIndirectionPosition {
   int index;
 
   IndirectionPosition() { this = TIndirectionPosition(index) }
 
-  string toString() {
+  override string toString() {
     index = -1 and
     result = "this"
     or