Use gitoxide in get_commits_info and get_commit_info

[cruessler]

• Implement From<gix::ObjectId> for CommitId
• Use gitoxide in get_commits_info and get_commit_info

This PR changes get_commits_info and get_commit_info to use gitoxide under the hood. It does not explicitly change any behaviour, although there possibly are subtle differences that I’m not aware of.

This implementation doesn’t log an error when either author or committer cannot be resolved using mailmap as the underlying implementation returns Option<Signature> instead of Result<Signature>. If you want, I can change that, though.

I decided to duplicate the logic of get_message into gix_get_message, using a prefix for the time both implementations are required.

I did not attempt to re-organize any of the code. My plan is to convert more functions to gitoxide before making any changes in that direction.

I followed the checklist:

• I ran make check without errors
• I tested the overall application