Auto merge of #116195 - fmease:rustdoc-investigate-perf-regression, r=GuillaumeGomez

rustdoc: speed up processing of cross-crate fns to fix a perf regression

* The first commit doesn't affect perf but get's rid of a `.clone()` and a bunch of lines of code. I can drop it if you'd like me to
* The second commit, *“reduce the amount of `asyncness` query executions”*, addresses the perf regression introduced in #116084

r? `@ghost`

Author: bors