Make `ChunkItem`s reference only `OutputAssets` (#73824)
This:
- Changes `ChunkItem`’s `references` implementation to only allow items
to reference `OutputAssets`
- Implements a default `references` that returns an empty set of output
assets
- Updates logic for using these output assets in `make_chunk_group`
- [x] Moves logic for using the inner module’s references into areas
that need it
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Co-authored-by: Tobias Koppers <tobias.koppers@googlemail.com>
Co-authored-by: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
