C#: Add some model generator examples for higher order methods.

Author: michaelnebel

csharp/ql/test/utils/modelgenerator/dataflow/Summaries.cs

@@ -506,10 +506,15 @@ public string M1(string s, Func<string, string> map)
         return s;
     }
 
-    public object M2(Func<object, object> map, object o)
+    public object Map(Func<object, object> map, object o)
     {
         return map(o);
     }
+
+    public void Apply(Action<object> action, object o)
+    {
+        action(o);
+    }
 }
 
 public abstract class BaseClass