Draft: Delegate outline generation to Merlin

[Tim-ats-d]

Replacement of the in-house solution for generating outlines by Merlin.

I had to regenerate the tests because merlin and ocaml-lsp don't calculate the positions of elements in the outline in the same way. Fir instance, the y loc was the enclosing location for ocaml-lsp:

let x = object
  method y = 10
(*^^^^^^^^^^^^^*)  
end

While Merlin indicates the exact position:

let x = object
  method y = 10
      (* ^ *)  
end

The PR diff also indicates that several items kind value have changed from 7 to 13. Indeed, Merlin treats instance variables as Values and not as Property like ocaml-lsp does. This change simply means that the icon displayed on the vscode side will be different

Could you please mark this PR has draft? We have to wait for the next Merlin next because we need this patch ocaml/merlin#1936

[xvw]

What a nice PR! Thanks!

[voodoos]

Sometime the result spans multiple lines like the previous one for a. But sometimes the only highlight the character like this one for b. Do you know why ?

I expect for most editors this is not an issue since they only use the start position ? But we might want to be a bit more careful about what we return here...