Draft: Upgrade to Vue 3

What does this MR do and why?

• Upgrade to Vue 3 with @vue/compat.
• Upgrade to Eslint 10.x and related fixes

Still to do:

• Get Jest tests working (see this commit as an example for required changes) (@platteier)
• Search result panel is missing styles (@HiruFernando12)
• Tabs don't render on pages with 2+ sets of tabs (first set renders; others do not) (@sarahgerman)
• Review deprecation warnings on Jest tests, and see if we can re-enable jest-fail-on-console (@sarahgerman)

Screenshots, screen recordings, or links to review app

No visual changes.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment.
2. Check out this branch.
3. Run make setup to update dependencies
4. Run make view to browse the site

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.