Add stub for `item` function. (#8363)
Add stub for `item` function. (#8363)

- Implement a `item` function like the StyleSheetList should have.
- Resolves #8349
darkreader/darkreader,darkreader/darkreader,alexanderby/darkreader,alexanderby/darkreader,darkreader/darkreader,alexanderby/darkreader