Migrate to pnpm

[philipp-spiess]

To be consistent with the defaults of the Tailwind V4 repo, I figured it might make sense to also migrate the intellisense extension to use pnpm as the default version manager.

This was mostly motivated by me doing a clean npm install in the workspace root but that causes a lot of packages to be missing within packages/vscode-tailwindcss (e.g. the concurrently module) so builds wouldn't just work. 😬

[thecrypticace]

I've fixed all the TypeScript issues, test issues, etc…

So only thing now is figuring out how to replace the workspace:* bit from the package.json of the packaged extension. It's only dev deps so won't ever actually be installed. And maybe it's not an issue at all but I'm not sure I'd count on that being future proof.

[thecrypticace]

From what I can tell in my testing the workspace:* deps in dev dependencies don't break the built VSIX file. So I think the best option here is to merge and see if the marketplace extension validation complains for insiders builds.

[thecrypticace]

I don't really like that these deps have to be at the root package level but it's happening because the shared esbuild.mjs file is at the root level rather than having an exact copy inside each package.

[philipp-spiess]

@thecrypticace thanks for fixing this up :)