Type.IsAssignableFrom works incorrect in special cases

[Igor Kiselev]

Type.IsAssignableFrom works incorrect for nullable and arrays:

using JSIL.Meta;
using JSIL.Proxy;
using System;

public static class Program
{
    public static void Main(string[] args)
    {
        Console.WriteLine(typeof(Struct?).IsAssignableFrom(typeof(Struct)) ? "true" : "false");
        Console.WriteLine(typeof(Struct).IsAssignableFrom(typeof(Struct?)) ? "true" : "false");

        Console.WriteLine(typeof(object[]).IsAssignableFrom(typeof(Struct[])) ? "true" : "false");
        Console.WriteLine(typeof(Struct[]).IsAssignableFrom(typeof(object[])) ? "true" : "false");

        Console.WriteLine(typeof(object[]).IsAssignableFrom(typeof(Class[])) ? "true" : "false");
        Console.WriteLine(typeof(Class[]).IsAssignableFrom(typeof(object[])) ? "true" : "false");
    }
}

public class Class { }
public struct Struct { }

public class Base { }
public class Derived1 : Base { }
public class Derived2 : Base { }

The easiest way to fix it will be add several more special cases in JSIL.MakeType assignment of typeObject._IsAssignableFrom, but it will duplicate logic of CheckType method for arrays/nullables. Probably we need some generic solution here.

EDITED: I believe we should move _IsAssignableFrom into JSIL.MakeCastMethods, or just remove_IsAssignableFrom at all and fully implement IsAssignableFrom inside System.Type.js