anchor.diff:   * considered accessible (and hence which take precedence over extensions) are
    * the members on Object.
    *
  - * @description Check that instance members have precedence over extension
  - * members of nullable type
  + * @description Check that instance members have no precedence over extension
  + * members of nullable type (if they are not members of Object)
    * @author sgrekhov@unipro.ru
    * @issue 41349
    */
  
positive.code:   void set setter(String v) {
      m = v;
    }
    String method(int i) => "$i";
    void operator[]=(int index, String value) {
      m = "[$index]=$value";
    }
  }
  
negative.code:   void set setter(String v) {}
    void set m(String v) {}
    String method(int i) => "Extension: $i";
    void operator []=(int index, String value) {}
  }
  
  main() {
    C? c = new C();
    Expect.equals("Extension getter", c.getter);
    c.m = "Lily was here";
    Expect.equals("m getter", c.m);
    c.setter = "Run, Forrest, run";
    Expect.equals("m getter", c.m);
    Expect.equals("Extension: 42", c.method(42));
    c[42] = "xxx";
    Expect.equals("m getter", c.m);
  }
  