Add files via upload

Author: RexJaeschke

tools/example-templates/additional-files/CallerArgumentAttrM.cs

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+using System;
+using System.Runtime.CompilerServices;
+#nullable enable
+class Test
+{
+    public static void M(int val = 0, [CallerArgumentExpression("val")] string? text = null)
+    {
+        Console.WriteLine($"val = {val}, text = <{text}>");
+    }
+}