C#: Add member flow example.

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

@@ -576,3 +576,24 @@ public class Inheritance
     }
 }
 
+public class MemberFlow
+{
+    public class C
+    {
+        public string Prop { get; set; }
+
+        public string Field;
+    }
+
+    // SPURIOUS-neutral=Models;MemberFlow;M1;(Models.MemberFlow+C);summary;df-generated
+    public string M1(C c)
+    {
+        return c.Prop;
+    }
+
+    // summary=Models;MemberFlow;false;M2;(Models.MemberFlow+C);;Argument[0];ReturnValue;taint;df-generated
+    public string M2(C c)
+    {
+        return c.Field;
+    }
+}