C#: Add tests with missing flow through dynamic members.

Author: MathiasVP

csharp/ql/test/library-tests/dataflow/fields/L.cs

@@ -0,0 +1,31 @@
+using System;
+
+public class L
+{
+    public string f1 { get; set; }
+    public string f2 { get; set; }
+    public string f3 { get; set; }
+
+    private void M1()
+    {
+        // dynamic write followed by dynamic read
+        dynamic d1 = this;
+        d1.f1 = Source<string>(1);
+        Sink(d1.f1); // $ MISSING: hasValueFlow=1
+
+        // dynamic write followed by static read
+        dynamic d2 = this;
+        d2.f2 = Source<string>(2);
+        L l2 = d2;
+        Sink(l2.f2); // $ MISSING: hasValueFlow=2
+
+        // static write followed by dynamic read
+        this.f3 = Source<string>(3);
+        dynamic d3 = this;
+        Sink(d3.f3); // $ MISSING: hasValueFlow=3
+    }
+
+    public static void Sink(object o) { }
+
+    static T Source<T>(object source) => throw null;
+}