Fixes #11291

See commits for a bit of a story to how we got here.

There's a couple things of note that aren't recorded in the diff very well:

• We bring in canvas for the COLR checks to pass (and upgrade our jsdom environment to pull it in correctly).
• We use a fake indexeddb so we can do indexeddb things.
• We have to map some modules to things to fix i18n, the number of copies of react we're running, etc
• The tests take about 166 seconds to run on my machine (i9-9900k, many RAM) - they surely take longer on CI.