Summary:
Upgrades Yarn to version 2 following [these instructions](https://yarnpkg.com/getting-started/migration). Doesn't add PnP just yet since that's big enough for its own diff.
Results: a noticeably faster but not lightning-fast install; slightly faster build; bundle runs a bit smoother in the browser too (this is partly due to dropping `@pixie-labs/components` earlier).

Test Plan: `yarn install && yarn dev`. `yarn test`. Everything should work as it did before, but a bit faster and smoother.

Reviewers: michelle, vihang, #third_party_approvers

Reviewed By: michelle, #third_party_approvers

JIRA Issues: PC-828

Differential Revision: https://phab.corp.pixielabs.ai/D8897

GitOrigin-RevId: 0ba438cdd31f30bba871da860cf00e26670e766e