[Unit tests] Migrate from `@web/test-runner` to `vitest`

[jpzwarte]

Provide a general summary of the issue here

Some problems we're having with wtr:

• using sinon in tests that then fail will cause a 120second timeout in wtr --watch; only workaround is running in debug mode with Chrome open
• @open-wc/testing causes typing issues and as a result linting errors that are unexplainable
• wtr is unmaintained; vitest is not
• better vscode integration with vitest
• better storybook integration with vitest

👤 Your name

Jeroen

🧢 Your Product/Team

SLDS