Allow nameof() expressions to use unbound generic types, like typeof does.

[otac0n]

This would enhance specific generic math scenarios:

if (definition == typeof(IPowerFunctions<>))
{
    var argTypes = typeArgs[..^1];
    var pow = type.GetMethod(nameof(IPowerFunctions<>.Pow), argTypes); // This is an error, but I don't have a type to fill in and nowhere else to pull the "Pow" string.
    this.Add(MakeLambda(argTypes, p => Expression.Call(pow, p[0], p[1])), WellKnownFunctions.Power);
}

[ufcpp]

Dup of #8480 and it is already merge into Visual Studio 17.13p2.