C#: Add list pattern sample file.

Author: michaelnebel

csharp/ql/test/library-tests/csharp11/ListPattern.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+
+class ListPattern
+{
+    public void M1(int[] x)
+    {
+        if (x is []) { }
+        if (x is [1]) { }
+        if (x is [_, 2]) { }
+        if (x is [var y, 3, 4]) { }
+        if (x is [5 or 6, _, 7]) { }
+        if (x is [var a, .., 2]) { }
+        if (x is [var b, .. { Length: 2 or 5 }, 2]) { }
+    }
+
+    public void M2(string[] x)
+    {
+        switch (x)
+        {
+            case []:
+                break;
+            case ["A"]:
+                break;
+            case [_, "B"]:
+                break;
+            case [var y, "C", "D"]:
+                break;
+            case ["E" or "F", _, "G"]:
+                break;
+            case [var a, .., "H"]:
+                break;
+            case [var b, .. var c, "I"]:
+                break;
+            default:
+                break;
+        }
+    }
+}