feat(vitest): add vitest cleanup export

[mcous]

Overview

This is the first PR in a series to add multiple Svelte versions and test runners to our CI test matrix.

1. 294 <-- you are here

2. 295

3. TODO add multiple Vitest environments to CI matrix
4. TODO add Jest to CI matrix

Change log

This PR concentrates on getting Vitest fully working, since there are a few issues with the setup

• Add @testing-library/svelte/vitest import, inspired by @testing-library/jest-dom/vitest to run auto-cleanup when using Vitest in non-global mode
  • Will require a docs update at some point
• Upgrade testing-library/jest-dom so we can use @testing-library/jest-dom/vitest
• Fix test scripts for watch mode and snapshot updates, which were still written with jest arguments
• Fix Vitest coverage reports, which were not being generated in CI

Review requests

~I'm keeping this PR in draft mode until I can verify that the @testing-library/svelte/vitest import works in a real project. Importing vitest in library code has given me issues before, so I want to verify before this is merged/released. It definitely works for our own test suite, though!~ Verified, works like a charm

[github-actions[bot]]

:tada: This PR is included in version 4.1.0 :tada:

The release is available on:

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

Your semantic-release bot :package::rocket: