Upgrade to Jest 27

Created by: umpox

Description

This PR:

• Upgrades jest from 26.6.3 to 27.5.1
• Removes most of the duplicated code in our fork of jest-environment-jsdom. We can just extend that import and make the manual changes ourselves.
• Removes unused Jest config in web/package.json that was duplicated

Notable changes:

• This now means that Jest no longer buffers and prints console messages at the top, which was a fundamental problem when evaluating Mocha vs Jest: https://github.com/sourcegraph/sourcegraph/issues/31630
• We're now using jest-circus (by default in Jest 27), it should "improve error messages, maintainability, and extensibility."

Test plan

• Run the tests, check everything still passes. ✅ CI Build
• Run this branch prefixed with main-dry-run to check full CI build. ✅ CI Build