Add ref forwarding for next/image with integration test
- fixes https://github.com/vercel/next.js/discussions/42885
- fixes https://github.com/vercel/next.js/issues/18398 (this one was closed with `onLoadingComplete`)
## Feature
- [x] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [x] Documentation added
Co-authored-by: Steven <229881+styfle@users.noreply.github.com>