Support for mailmap

[harrisric]

Description

Hi,
It's not explicitly noted as an exclusion/omission but JGit does not appear to support mailmap.

Motivation

This repo has its own .mailmap file which I think gives a general indication of the utility of this feature to allow corrections to or subsequent changes of names/emails.

Alternatives considered

No response

Additional context

No response

[tomaswolf]

There is a change chain from 2019 implementing this. Not sure what the state is; looks a bit as if this fell through the cracks. It was never merged? There are some still open review comments (although they are shown as "resolved"; that might be an issue with moving the git repo between Gerrit instances). In any case this would need to be rebased, conflicts resolved, and "since" annotation need to be updated.

[msohn]

I rebased and reworked the old change series adding mailmap support. Please review it.