style: format the markdown and lint against it in ci

[simonsan]

To make future diffing easier and adopt a common style over the whole codebase.

This is essentially our dprint.json from https://github.com/rust-unofficial/patterns/blob/main/dprint.json

I think it would make it easier to merge these changes from #1817

TODO:

• Does it affect the translations as line numbers change, or does parse the markdown directly?

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @marioidival (or someone else) some time within the next two weeks.

[simonsan]

@mgeisler Does this reformatting affect the mdbook-i18n-helper translations as line numbers change, or does parse it the markdown directly and this reformatting would be OK to do?

[mgeisler]

@mgeisler Does this reformatting affect the mdbook-i18n-helper translations as line numbers change, or does parse it the markdown directly and this reformatting would be OK to do?

Reformatting is fine! Version 0.2 of mdbook-i18n-helpers started normalizing the whitespace when extracting messages, so you won't see any change to the translations.

With version 0.3, we started to only extract string literals and comments from Markdown code blocks, so reformatting them will now also be invisible to the translations. You should run the mdbook-i18n-normalize tool on your existing translation files if you have files from version 0.1 that you need to migrate.