C#: Add a test for type alias.

csharp/ql/test/library-tests/typealias/alias.cs

@@ -0,0 +1,30 @@
+using System;
+
+using TupleType1 = (int, object);
+using TupleType2 = (int, string);
+using TupleType3 = (int, object);
+using Point = (int x, int y);
+
+public class TupleMethods
+{
+    public void M1(TupleType1 t)
+    {
+        var x = t.Item1;
+        var y = t.Item2;
+    }
+
+    public void M2(TupleType2 t)
+    {
+        var x = t.Item1;
+        var y = t.Item2;
+        M1(t);
+    }
+
+    public void M3(Point p)
+    {
+        var x = p.x;
+        var y = p.y;
+    }
+
+    public void M4(TupleType3 t) { }
+}

csharp/ql/test/library-tests/typealias/alias.expected

@@ -0,0 +1,4 @@
+| alias.cs:10:17:10:18 | M1 | alias.cs:10:31:10:31 | t | (Int32,Object) |
+| alias.cs:16:17:16:18 | M2 | alias.cs:16:31:16:31 | t | (Int32,String) |
+| alias.cs:23:17:23:18 | M3 | alias.cs:23:26:23:26 | p | (Int32,Int32) |
+| alias.cs:29:17:29:18 | M4 | alias.cs:29:31:29:31 | t | (Int32,Object) |

csharp/ql/test/library-tests/typealias/alias.ql

@@ -0,0 +1,8 @@
+import csharp
+
+from Method m, Parameter p, Type t
+where
+  m.fromSource() and
+  p = m.getAParameter() and
+  p.getType() = t
+select m, p, t.toString()