C#: Add sample code file that calls both supported and unsupported library code with respect to flow summaries.

csharp/ql/test/query-tests/Telemetry/LibraryUsage/ExternalLibraryUsage.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+
+public class LibraryUsage
+{
+    public void M1()
+    {
+        var l = new List<object>(); // Uninteresting parameterless constructor
+        var o = new object(); // Uninteresting parameterless constructor
+        l.Add(o); // Has flow summary
+        l.Add(o); // Has flow summary
+    }
+
+    public void M2()
+    {
+        var d0 = new DateTime(); // Uninteresting parameterless constructor
+        var next0 = d0.AddYears(30); // Has no flow summary
+
+        var d1 = new DateTime(2000, 1, 1); // Interesting constructor
+        var next1 = next0.AddDays(3); // Has no flow summary
+        var next2 = next1.AddYears(5); // Has no flow summary
+    }
+
+    public void M3()
+    {
+        var guid1 = Guid.Parse("{12345678-1234-1234-1234-123456789012}"); // Has no flow summary
+    }
+}