FR: Type checking for DOM methods

Calling something like `el.appendChild('hello')` is invalid and normally throws

```Uncaught TypeError: Failed to execute 'appendChild' on 'Node': parameter 1 is not of type 'Node'.```

In WorkerDOM, however, the error is a lot more ambiguous:

```Uncaught TypeError: t.remove is not a function```

While this is a developer error, it took me a while to figure out what's wrong. I think stronger type checking would help with the developer experience here.