build: maybe use npm workspaces

[davidjgoss]

Summary

Npm 7 has a new workspaces feature to support projects with multiple libraries.

The documentation is pretty sparse at this point, but anyway:

• https://github.com/npm/rfcs/blob/latest/implemented/0026-workspaces.md
• https://docs.npmjs.com/cli/v7/using-npm/workspaces

I think this might be a good fit for the monorepo, in terms of:

• Declaring and installing common tooling dependencies like typescript and eslint once at the root level
• Reliably linking between dependencies locally

Wanted to get any initial feedback before I start experimenting, especially potential downsides. One I think would need to be addressed would be how to continue supporting building a subset of the monorepo for just a particular package.

Thanks!

[aslakhellesoy]

This is done!