Instead of repeating the same logic by walking HIR during metadata encoding.
The only difference is that we are no longer encoding `macro_rules` items, but we never currently need them as a part of this list.
They can be encoded separately if this need ever arises.
`module_reexports` is also un-querified, because I don't see any reasons to make it a query, only overhead.
Lower them into a single item with multiple resolutions instead.
This also allows to remove additional `NodId`s and `DefId`s related to those additional items.
