Support more generics in callvirt handler

[puff]

Callvirt doesn't support devirtualizing methods with generic parameters, or finding explicit method implementations using generics in.
Thus, this code will error:

var module = ModuleDefinition.FromModule(typeof(Usage).Module);
var method = module.GetAllTypes().First(x => x.Name == "Usage")?.Methods.First(x => x.Name == "Use");
var vm = new CilVirtualMachine(module, false);
vm.Invoker = DefaultInvokers.StepIn;

var thread = vm.CreateThread();
var ret = thread.Call(method!, Array.Empty<BitVector>());
Console.WriteLine(Usage.Use() == ret!.AsSpan().I32);
vm.DestroyThread(thread);

public interface ITestInterface<T>
{
    public T TestMethod<U>(T i, U u)
    {
        return i;
    }
}

public class TestClass<C> : ITestInterface<int>
{
    int ITestInterface<int>.TestMethod<U>(int i, U u)
    {
        return i;
    }
}

public static class Usage {
    public static int Use()
    {
        var tc = new TestClass<long>();
        var leet2 = ((ITestInterface<int>)tc).TestMethod<short>(1337, 2);
        return leet2;
    }
}

This PR fixes it by instantiating generics before comparison, and when returning the devirtualized result.
I also removed the baseMethod.IsVirtual check as it prevents the code from executing as well.
EDIT: Re-added the baseMethod.IsVirtual check, I got confused with it earlier :P

[Washi1337]

Thanks!