🛠️ Repo: Consider adding a sentences-per-line linter

[JoshuaKGoldberg]

Tooling Suggestion Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest master branch of the repository.
• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

I'm a fan of roughly enforcing that Markdown docs keep to one sentence per line. This is useful because:

• Shorter lines result in simpler, easier-to-understand Git diffs
• Longer lines are harder to read in source code

In #5038 I switched a large percentage of the Mocha docs to use that. It'd be nice to enforce this preference - if and only if we agree we like it.

Additional Info

Mentioned by @voxpelli in #5038 (comment).

Right now, https://github.com/JoshuaKGoldberg/sentences-per-line is a markdownlint plugin. We don't use markdownlint (yet?) and per JoshuaKGoldberg/create-typescript-app#567 I'd be very interested in using eslint-plugin-mdx for linting .md instead. TBD.

This isn't a very high priority item IMO. I'm not listing it in the Maintenance Reboot project. Someone yell at me if we actually should treat this with any urgency. 😄