Use node version 16

[victorlin]

(preview)

Summary of changes

• Update version references
• Regenerate package-lock.json file with npm 8 (now uses lockfile v2¹)

¹ https://github.blog/2021-02-02-npm-7-is-now-generally-available/#changes-to-the-lockfile

I chose to regenerate package-lock.json (remove and re-run npm install) because I was getting weird errors with the recommended approach of running npm install to update the existing lockfile:

npm ERR! node-pre-gyp ERR! install response status 404 Not Found on https://github.com/Automattic/node-canvas/releases/download/v2.8.0/canvas-v2.8.0-node-v93-darwin-unknown-arm64.tar.gz 
…
npm ERR! Package pangocairo was not found in the pkg-config search path.
npm ERR! Perhaps you should add the directory containing `pangocairo.pc'
npm ERR! to the PKG_CONFIG_PATH environment variable
npm ERR! No package 'pangocairo' found
npm ERR! gyp: Call to 'pkg-config pangocairo --libs' returned exit status 1 while in binding.gyp. while trying to load binding.gyp
npm ERR! gyp ERR! configure error 
npm ERR! gyp ERR! stack Error: `gyp` failed with exit code: 1

I think regenerating is fine as long as we test the preview build thoroughly to make sure everything still works as expected.

Related issues

Checklist

• [x] Fix npm ci issues
• [ ] Add tests or provide evidence of manual testing (if applicable)
• [x] PR checks pass (see CONTRIBUTING.md for how to fix failing checks)

[victorlin]

I clicked around the preview and all the pages from the toolkit seem to be on par with the currently deployed site. Going to merge this now.