Self contained mode

Hello,

I am trying to create a self contained xll pack so that users dont need to update dotnet runtime everytime dotnet is upgraded. I have playing with addin and csproj option with no luck.

I saw [this issue](https://github.com/Excel-DNA/ExcelDna/issues/697), but my error is different I am getting an exception in the runtime
```
System.MissingMethodException: Method 'ExcelDna.Loader.XlAddIn.Initialize' not found. at System.RuntimeType.InvokeMember
```

So my question is, is it possible to create a self-contained xll pack, if so how?