Improvements to prettify

[palas]

Changelog

- description: |
     Added support for relative files and rebasing to the prettify tool, and add new checks on arguments
# uncomment types applicable to the change:
  type:
  - maintenance    # not directly related to the code

Context

When rebasing there was no option of prettify that would work (because changes while rebasing are neither staged nor unstaged, they are in the previous commit). So this PR adds an option -p that diffs against HEAD~1.

Also the tool would not work unless run from the top level in the repo, which is kind of inconvenient. So this change make prettify work from any subfolder.

This PR also imports changes from cardano-cli that improve checks on arguments (to give better error messages), and simplifies tool availability checking.

Twin PR #842 in cardano-cli

How to trust this PR

Probably testing is the best way to ensure it works. But they are few changes, so a quick look at the diff would also be nice.

Checklist

• [x] Commit sequence broadly makes sense and commits have useful messages
• [x] New tests are added if needed and existing tests are updated. See Running tests for more details
• [x] Self-reviewed the diff