Double check editor integration

[zth]

Make sure that the editor experience using Core is as good as possible.

• Ensure that hovers make sense. E.g. we see no Core__Array.t<'typ>, but always array<'typ>, for builtins.

[cknitt]

It would be quite useful if this could be a general thing for aliases to basic types like string, array etc.

E.g. always show string instead of Js.String.t, Js.String2.t, Belt.String.t, Belt.Map.String.key etc.

[zth]

Yes, for sure, I agree

[zth]

Module level docstrings would be nice here too. Ie if you hover a module, you currently don't see the module level documentation.