chore: clean up dependencies, spell check caching, and leftover markup - #4833

Issue URL: N/A

What is the current behavior?

A few small leftovers: a spell check that re-reads every file, a dependency used once, a heading level skip on the glossary, dependency install scripts nobody reviewed, and dead markup from older versions of the site.

What is the new behavior?

• npm run spellcheck uses --cache, so a repeat local run takes 4s instead of 12s. .cspellcache is gitignored
• fs-extra is removed. scripts/release-notes.mjs was its only user and now writes the same JSON with fs.writeFileSync
• Glossary terms are ## instead of ###, so the page no longer jumps from the h1 to h3. Anchors are unchanged
• allowScripts in package.json denies install scripts for the 4 dependencies that have them. None are needed:
  • @parcel/watcher and fsevents ship prebuilt binaries
  • @swc/core only checks its prebuilt binary and downloads a WASM fallback if that fails
  • core-js prints a funding message
• Removed dead markup in current and v8 docs:
  • the glossary's <div id="what-is">, left over from the pre-Docusaurus site
  • <intro-end /> on 4 pages, which nothing styles or reads

Does this introduce a breaking change?

• Yes
• No

Other information

npm only reports allowScripts today and will enforce it in a future release. To check that enforcement won't break anything, I installed with npm ci --ignore-scripts and built the site. The swc, parcel watcher and fsevents bindings all load.

Apart from the removed tags, the intro-end pages build to the same HTML.

The glossary terms now render at h2 size. Preview: Glossary