Experiment with Yarn 2

[TimothyGu]

Yarn 2 has been released, supposedly bringing in a bunch of enhancements. See https://dev.to/arcanis/introducing-yarn-2-4eh1, a blog post by the lead maintainer of Yarn 2. This bug is to track our progress in experimenting and hopefully eventually adopting Yarn 2.

Some differences:

• Different and non-backwards-compatible yarn.lock format
• Stricter dependency requirements
• No node_modules anymore!
• Yarn is now installed per project

[TimothyGu]

Here are some of my findings:

• It works.
• It does away with node_modules as advertised.
• And, it's very slow.

I think we might want to take another look deeper into the future, like when a non-RC version of Yarn 2 gets released. But for now, I will unassign myself.