Auto merge of #83828 - camelid:rustdoc-vec-perf, r=jyn514
Auto merge of #83828 - camelid:rustdoc-vec-perf, r=jyn514

rustdoc: Use `ThinVec` in a few places

Almost every crate has no primitives and no keywords defined in it, so
using `ThinVec` should make some types smaller.

aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust