Rollup merge of rust-lang#146070 - notriddle:skip-loading-function-data, r=GuillaumeGomez

rustdoc-search: skip loading unneeded fnData

Fixes rust-lang#146063 (probably)

Based on the test I ran, it seems like most of the CPU time is being spent loading function signature data. This PR should avoid that.

https://notriddle.com/rustdoc-html-demo-12/skip-loading-function-data/doc/std/index.html

Author: GuillaumeGomez