feat: support parsing existing package.json descriptions as markdown

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: Parse description as markdown (in addition to HTML) #1934
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Makes parsing around HTML (README.md) vs. markdown (package.json) descriptions smarter. marked in inline mode is used to parse existing package.json descriptions, before they're checked against the README.md one.

Also normalizes the output package.json's description to be plain text, since neither GitHub nor npm support rich text (#1934 (comment)). Example improvement: JoshuaKGoldberg/eslint-plugin-erasable-syntax-only@c43f07b

🎁

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.81%. Comparing base (11d8e05) to head (a9981c1).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2132   +/-   ##
=======================================
  Coverage   99.81%   99.81%           
=======================================
  Files         129      129           
  Lines        5425     5449   +24     
  Branches      387      391    +4     
=======================================
+ Hits         5415     5439   +24     
  Misses         10       10           

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[github-actions]

🎉 This is included in version v2.26.0 🎉

The release is available on:

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

Cheers! 📦🚀