[WIP] Add a --solver-log-format internal-json option that make cabal-install solver config log output machine-readable

[yvan-sraka]

This PR modifies the cabal-install CLI behavior by adding a new alternative JSON output that allows the cabal-install solver logs to be mechanized, e.g., similar to the tree view provided by nix-output-monitor for Nix (nix-build --log-format internal-json). It's a follow-up of #9159.

Checklist:

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.

Bonus points for added automated tests!

[mpickering]

Have you already developed the tool to consume this output? I don't see there is any hurry to merge this patch before you've also tried to implement the consumer of this tool -- that way you can more easily iterate on the json message format whilst developing the tool to visualise the output (in case more or different information is needed)

[mpickering]

Currently missing documentation update and changelog.

[mpickering]

So far the patch doesn't implement any of the JSON logic. It seems that the refactoring to use SolverTrace rather than String would be worthwhile in any case, so we could separate that out and land that first.

[andreabedini]

A related (overlapping?) PR is #9159

[yvan-sraka]

Thanks, @mpickering, for your feedbacks, as mentioned by @andreabedini, this PR is rebased on top of #9159 that should be reviewed first (and is the so called SolverTrace refactoring), so I will answer your comments and apply your suggestions to that PR instead! Also, you're right, there is not any hurry to merge this patch, I marked this PR as draft, and I could rework it in parallel of experimenting with a consumer tool of the not-yet-implemented alternative output.