Auto merge of rust-lang#96135 - petrochenkov:doclink6, r=GuillaumeGomez

rustdoc: Optimize and refactor doc link resolution

One more subset of rust-lang#94857 that should bring perf improvements rather than regressions + a couple more optimizations on top of it.
It's better to read individual commits and their descriptions to understand the changes.
The `may_have_doc_links` optimization is not *very* useful here, but it's much more important for rust-lang#94857.

Closes rust-lang#96079

Author: bors

proc_macro/Cargo.toml

@@ -5,3 +5,7 @@ edition = "2021"
 
 [dependencies]
 std = { path = "../std" }
+# Workaround: when documenting this crate rustdoc will try to load crate named
+# `core` when resolving doc links. Without this line a different `core` will be
+# loaded from sysroot causing duplicate lang items and other similar errors.
+core = { path = "../core" }