git: add diff-highlight diff pager option

[aymanbagabas]

Description

This adds a new diff-highlight option to make use of the simple included git diff highlighter that comes with canonical git. diff-highlight is a perl script that high lights the changes in changed lines. This makes it human-readable and easy to see changes in diffs.

For more info, see https://github.com/git/git/blob/master/contrib/diff-highlight/README

This was inspired by #2882 and #2850

Before:

After:

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

CC/ @rycee @ncfavier

[rycee]

Thanks! Merged to master now 🙂