[next] refactor(useIsFullscreen): migrate to Typescript

[susnux]

• For [FR]: TypeScript support #841

☑️ Resolves

• Migrate to Typescript for the types

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 3️⃣ Backport to next requested with a Vue 3 upgrade

[ShGKme]

/backport to stable8

[backportbot]

The backport to stable8 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable8
git pull origin stable8

# Create the new backport branch
git checkout -b backport/6659/stable8

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 132b1edd

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/6659/stable8

Error: Failed to check for changes with origin/stable8: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.