Migration to Yarn 2 and Enforcing Node >= 10

[talam]

Yarn 2 was recently released with various updates that we would benefit from. Let's migrate over to it as part of CC 1.3 and also consider if there are other config updates we want to make to our default yarn setup (e.g. use of --frozen-lockfile during installs). Yarn 2 also doesn't support Node 8 anymore so we can use the opportunity to remove Node 8 support from CC.

cc @sklose

[emmalynch]

This is blocked by the following yarn issue: https://github.com/yarnpkg/yarn/issues/7890

[sklose]

@emmalynch is this only blocked for going from 1.21 -> 1.22 or also for upgrading all the way to v2?

If it's completely blocked, then let's limit the scope of the PR you already started to just remove node 8 support + add the --frozen-lockfile flag ... we can do the yarn upgrade later then once that ticket is resolved.

[emmalynch]

I was able to work around that issue thankfully.

However, there is an outstanding issue with docusaurus, which will probably require us to upgrade that to v2 before we can use pnp though: https://github.com/yarnpkg/berry/issues/818#issuecomment-580871488

For the moment, I've gone ahead and switched to the node-modules linker, so at least we can upgrade to v2 & remove support for node 8.