[ts-next-plugin] auto import metadata type (#78258)
Follow up of https://github.com/vercel/next.js/pull/78237
Auto import the `Metadata` type when completing the `metadata` and
`generateMetadata` option.
- If there is a `'use ...'` top directive, add import below the
directive.
- If there is an existing Metadata import, do not add another import.
- This includes aliases as well.
https://github.com/user-attachments/assets/5ea1ce7e-2320-41f0-ba33-af7568bbdd11
