Add a formatting step using mdformat as part of generate_mkdocs.py

[augustelalande]

Summary

The purpose of this change is mainly to address one of the issues outlined in #10427. Namely, some lists in the docs were not rendering properly when preceded by a text block without a newline character. This PR adds mdformat as a final step to the rule documentation script, so that any missing newlines will be added.

NB: The default behavior of mdformat is to escape markdown special characters found in text such as <. This resulted in some misformatted docs. To address this I implemented an ad-hoc mdformat plugin to override the behavior. This may be considered a bit 'hacky', but I think it's a good solution. Nevertheless, if someone has a better idea, let me know.

Test Plan

This change is hard to test systematically, however, I tried my best to look at the before and after diffs to ensure no unwanted changes were made to the docs.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.

[charliermarsh]

Thanks