RFR: GitRepository#revert does not work as intended

[Julian Waters]

The `Repository#revert` interface is meant to allow for rolling the Repository back to a specific commit, but the Git implementation in `GitRepository#revert` implements this via a checkout, which can cause issues, especially with newer versions of Git where it doesn't have any effect at all. More appropriate would be using `git restore --source` to implement the GitRepository variant instead, which is actually the encouraged way to do so nowadays

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Commit messages:
 - GitRepository#revert does not work as intended

Changes: https://git.openjdk.org/skara/pull/1450/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1450&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1450.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1450/head:pull/1450

PR: https://git.openjdk.org/skara/pull/1450