C#: Add line span pragma example.

Author: michaelnebel

csharp/ql/test/library-tests/csharp10/LinePragmas.cs

@@ -0,0 +1,12 @@
+using System;
+
+public class MyLineDirective
+{
+    public static void M1()
+    {
+#line (1, 1) - (1, 30) 5 "LinePragmasRef1.cs"
+        int i = 0;
+#line (2, 1) - (5, 32) "LinePragmasRef2.cs"
+        int j = 0;
+    }
+}