Fix for "dune external-lib-deps" command

[moyodiallo]

The new version of dune (from 3.0.0) removed "dune external-lib-deps" and this is a patch that work with a patch of dune from "https://github.com/moyodiallo/dune/tree/opam-dune-lint".

There's already a PR(ocaml/dune#6045) in dune about this patch, but not guarantee to be merged. The command may change also.

This could be a temporary solution for our CI projects.

@tmcgilchrist

[moyodiallo]

At the stage opam-dune-lint works using this dune PR ocaml/dune#6839.

This particular example is left for now, because dune describe external-lib-deps(far different to dune external-lib-deps) does not resolve it.

(executable{s}
  (name{s} prog)
  (libraries a b))

(install 
  (section bin)
  (package pkg)
  (files prog.exe))

• The solution that I have at the moment, is to solve those cases in opam-dune-lint.

[tmcgilchrist]

This could use more tests for the dune-file parsing since we no longer use dune's parser for files.
There is a risk that newer versions of dune introduce breaking format changes or interpretations of previous fields.

[moyodiallo]

I rewrite the PR, there was some error that I made.

At this stage there's 2 things left:

• correcting the test about tests/test_vendoring.t : It's to consider a public executable could have an internal private lib as a dependency which have an external dep lib.
• the install case Fix for "dune external-lib-deps" command #46 (comment)
• Take in consideration this case Allow dependencies for executables ocaml/dune#3499

[moyodiallo]

At this stage, it could be tested with this branch https://github.com/moyodiallo/dune/tree/opam-dune-lint-testing.
before the merge of ocaml/dune#7480 and ocaml/dune#7478.

[moyodiallo]

This issue #28 is now fixed in the current PR.

cc @tmcgilchrist

[MisterDA]

Some suggestions on coding style.

[smorimoto]

When will this be released?

[moyodiallo]

We are testing it on https://ocaml.ci.dev/ via opam lint jobs. When it seems stable, it will be released.