chore(vue3): replace `extends:` with `Vue.extend`

What does this MR do?

@vue/compat has an issue, when render functions coming from extends: in component are not patched

See https://github.com/vuejs/core/issues/6860 for details

Fixing this in vue core is not trivial, so we just swap it to Vue.extend

This is forward-compatible change to support @vue/compat #1981 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • CustomersDot: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.