Use PNPM and enforce js bundling in PR

[nick-fields]

Description

• Upgrade to pnpm because it's great
• Handle scenario where contribution's made entirely in GH UI are bundled properly
  • If a contributor makes a change via the GH UI and opens a PR for it, pre-commit hooks are skipped
  • When the same change is made locally, a pre-commit hook fires to bundle the code change to ensure that the code changed matches the bundled code that GHA requires to be committed
  • To handle this, we now bundle on every commit and if changes exist, commit the bundle

Testing

• No tests added, but the test will be if CI passes and the intentionally out of sync dist/index.js gets auto updated.

[xavier2k6]

Why not use v4 of pnpm/action-setup?
https://github.com/pnpm/action-setup/releases

You could also look into increasing pnpm?
https://github.com/pnpm/pnpm/releases