Fixes#93428
This fix is a response to a couple of special cases related to the
`module_id`, which is eventually used for trait candidates:
* The module id is always set to the current crate, when checking `crate::`.
Normally, the set of in-scope traits would be set in `load_links_in_attrs`,
but if there are no doc comments, then that loop will never run.
* the module id is set to the parent module, when resolving a module
that is spelled like this:
// Notice how we use an outlined doc comment here!
// [`Test::my_fn`]
mod something {
}
As with the above problem with `crate::`, we need to make sure the
module gets its traits in scope resolved, even if it has no doc comments
of its own.
