BREAKING CHANGE: upgrade to Lit 3

[dlockhart]

Note: this repo is only used by the media player... it would save a lot of effort in the long run if it could be merged into that repo at some point!

⚠️ DO NOT MERGE yet! ⚠️

👋 Hey, we're upgrading to Lit 3! 🎉 This PR prepares this repo for the upgrade, which will happen starting May 21st. Someone from team Gaudí will take care of everything (except approving this PR), so sit back and enjoy the upgrade!

A Phased Approach

Merges will happen in several phases based on where each repo sits in the overall dependency graph of Lit-related things.

This repo will be in phase: 2 of 10

Since this repo is in a downstream phase, its dependency versions that use Lit 3 haven't released yet, so its CI will be in a broken state. This will be resolved when the previous phase of upgrades completes.

Next steps

• CODEOWNERS approvals received 👍 (you can do that now to avoid holding up the upgrade later!)
• Wait until this repo's phase of the upgrade arrives ⌛
• Rebase from main / master to pick up latest changes
• If this repo has a package-lock.json, update to latest dependencies
• CI goes green ✅
• Merge & trigger a MAJOR version bump

[d2l-github-release-tokens]

🎉 This PR is included in version 3.0.0 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

Your semantic-release bot 📦🚀