Add custom elements language server for todo-app

[janechu]

Pull Request

📖 Description

This PR takes the changes from #6900 and applies them with some documentation and an update to the package lock instead of the previous yarn lock.

Thanks @matteematt! We are moving our default branch from master to main but I wanted to get your change in here. If you'd like to add some additional info to our documentation site that would be 💯.

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

[matteematt]

Hey all, thanks for getting this in - that's great to see! I am happy to update your documentation if you point me to where I need to go to make changes.

Also I just want to confirm with you that this is working with Fast v2? I haven't had chance to try it myself but that's great news if so

There is an issue with the underlying code parser which I am not sure that it fully supports some of the FAST v2 syntax open-wc/custom-elements-manifest#276