Custom implicit Ctype is not used in dynamic mode

VB can't call the implicit ctype operator on dynamic objects. This code gives the runtime error: Can't convert from Test To String:
```vb
Option Strict Off
Option Explicit On

Module Program
Sub Main()
Dim o As Object = New Test
Dim s As String = o
End Sub
End Module

Class Test
Public Shared Widening Operator CType(t As Test) As String
Return t.ToString()
End Operator
End Class
```

While the same code runs correctly in C#:
```c#
dynamic o = new Test();
string s = o;

class Test
{
public static implicit operator string (Test t) => t.ToString();
}
```

I think Vb should adapt the [C# spcs about this](https://github.com/dotnet/csharplang/blob/f63f70960c8c7d162eb645ad7ff0c891797995f9/spec/conversions.md#implicit-dynamic-conversions), after all vb was a dynamic langish since before .NET, where even declaring variables was not mandatort (Option Explicit Off was the default in old vb versions before dotnet.)
Also, I suggest that dynamically or not, vb should use .ToString to implicitly convert any type to a string as lomg as ther is no a suitable CType defined to do that. This is more like how VB does things.