Js__Js_xxx.t appears on type-errors and hovering

[davesnx]

Since we wrap melange.js there's an unfortunate side-effect of dune being wrapped by using a module name with __ like (Js__Js_date) for all modules inside Js like (js_date.ml).

It's very convenient to use wrapped modules when you don't want to expose a bunch of modules to the top-level, but since Js isn't meant to be opened at the top I would argue that it's better if we keep it unwrapped for the sake of having better error messages.