Switch from NPM to PNPM for package management

[rmunn]

Fixed issues

Fixes #1811. Fixes #1653. Fixes #1654.

Description

Switching to PNPM has a couple of advantages. The first is speed: pnpm install is typically faster than npm install, though how much will depend heavily the speed of your Internet connection. The second is disk usage: if you have multiple copies of the Language Forge repository on your disk, perhaps because you want to keep a copy of develop running while you work on a different branch in another folder, PNPM will de-duplicate the packages whose versions are the same between the copies (which will be 100% of them unless you're fiddling with package.json in your branch).

Screenshots

No visible changes.

Checklist

• [X] I have labeled my PR with: bug, feature, engineering, security fix or testing
• [X] I have performed a self-review of my own code
• [X] I have reviewed the title & description of this PR which I will use as the squashed PR commit message
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have enabled auto-merge (optional)

Testing

Testers, use the following instructions against our staging environment. Post your findings as a comment and include any meaningful screenshots, etc.

Describe how to verify your changes and provide any necessary test data.

• Run make
• If you get errors about pnpm not being found, run corepack enable then run make again.
• Go to http://localhost:8080/ and make sure the site still works.

[github-actions[bot]]

Unit Test Results

362 tests   362 :white_check_mark:  12s :stopwatch:  37 suites    0 :zzz:   1 files      0 :x:

Results for commit f9f550df.

:recycle: This comment has been updated with latest results.