Auto merge of #107054 - petrochenkov:effvisdoc3, r=GuillaumeGomez

rustdoc: Collect "rustdoc-reachable" items during early doc link resolution

This pass only needs to know about visibilities, attributes and reexports, so it can be run early, similarly to `compute_effective_visibilities` in rustc.
Results of this pass can be used to prune the list of extern impls early thus improving performance of https://github.com/rust-lang/rust/pull/94857.