dune describe should show a decent amount of information even on a project which doesn't build

[Khady]

Desired Behavior

So far except by parsing all dune related files by hand, the only way to get some information about a project seems to be dune describe. Unfortunately as soon as the project contains a piece of code which doesn't compile we don't get any information anymore. Given the architecture of dune it's expected that some things like the whole build graph can't be returned in that case, but there are many information that should still be available. And even the in a broken project returning at least the info about what leads to the error would be useful.

Example

Any project with either an error in an ocaml file or an opam dependency which isn't installed