Consider adding useful extension module

While the aspiration of this project is to have bindings for anything available in the browser, it might be interesting consider having an additional auxiliary module.

Or to phrase it differently: some API methods are shit. Like https://developer.mozilla.org/en-US/docs/Web/API/Document/createElement. You pass it any string and get an element back. Maybe you want to create something more specific and get a better type back like document.createElement("input") and get HTMLInputElement back.

So having something like:

type document

type htmlInputElement

@scope("document")
external createInputElement: (unit, @as("input") _) => htmlInputElement =
  "createElement"

let i = createInputElement()

The input string can't be misspelled and the return type is better.
Perhaps each current API module can have an APIExt companion module?
Let me know what you thoughts.

Review the existing API modules and the proposed createElement/createInputElement example. Decide the scope and design for any APIExt companion modules; done means the intended module structure and supported typed helpers are agreed and clearly specified.