Implement entities showing static virtual in interface

Author: BartoszKlonowski

docs/csharp/whats-new/tutorials/snippets/staticinterfaces/Duplicate.cs

@@ -0,0 +1,14 @@
+public struct Duplicate : IGetDuplicated<Duplicate>
+{
+    public int _num;
+
+    public Duplicate(int num)
+    {
+        _num = num;
+    }
+
+    public static Duplicate operator ++(Duplicate other)
+        => other with { _num = other._num + other._num };
+
+    public override string ToString() => _num.ToString();
+}

docs/csharp/whats-new/tutorials/snippets/staticinterfaces/GetDuplicated.cs

@@ -0,0 +1,4 @@
+public interface IGetDuplicated<T> where T : IGetDuplicated<T>
+{
+    static virtual T operator ++(T other) => throw new NotImplementedException();
+}