feat: move sentences-per-line from Markdownlint to Prettier

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: Move sentences-per-line into the formatter, Prettier #2216
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Uses prettier-plugin-sentences-per-line to move this formatting/style concern to the formatter. This creates a new blockPrettierPluginSentencesPerLine separate from Markdownlint.

As a tooling benefit, now the lint:md command doesn't have to add in a --rules.

This also applies the rule to CODE_OF_CONDUCT.md. I'd previously resisted because I didn't want to mess with the pre-provided copy&paste of the Contributor Covenant. But it's simpler to just apply the whitespace changes.

🎁

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.78%. Comparing base (32a8bb8) to head (f37fb82).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2285   +/-   ##
=======================================
  Coverage   99.78%   99.78%           
=======================================
  Files         136      137    +1     
  Lines        6123     6142   +19     
  Branches      511      511           
=======================================
+ Hits         6110     6129   +19     
  Misses         13       13           

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[github-actions]

🎉 This is included in version v2.49.0 🎉

The release is available on:

• GitHub releases
• npm package (@latest dist-tag)

Cheers! 📦🚀