Auto merge of #119912 - notriddle:notriddle/reexport-dedup, r=GuillaumeGomez

rustdoc-search: single result for items with multiple paths

Part of #15723

Preview: https://notriddle.com/rustdoc-html-demo-9/reexport-dup/std/index.html?search=hashmap

This change uses the same "exact" paths as trait implementors and type alias inlining to track items with multiple reachable paths. This way, if you search for `vec`, you get only the `std` exports of it, and not the one from `alloc`.

It still includes all the items in the search index so that you can search for them by all available paths. For example, try `core::option` and `std::option`, and notice that the results page doesn't show duplicates, but still shows all the items in their respective crates.

Author: bors