Rustdoc search does not find inherent methods on primitive types

[theemathas]

Searching on rustdoc for a inherent method on a primitive type (e.g. width) does not find it, even if it exists.

cc #23104.

[tomjakubowski]

Probably a search index bug. The relevant code is in rustdoc::html::render, specifically the fold_item method of impl DocFolder for Cache, and the build_index function.

[aturon]

triage: I-nominated ()

Nominating for P-high, 1.0

[pnkfelix]

P-high, 1.0.

[pnkfelix]

(this is a serious usability issue for clients of the language itself.)

[nrc]

cc @cmr in case you want to take this, otherwise I'll keep it on my radar