rustdoc: improve searching for duplicate functions of generic types

[calebzulawski]

This is coming from std::simd (rust-lang/portable-simd#191).

Consider searching std for Simd::abs: https://doc.rust-lang.org/nightly/std/simd/?search=Simd%3A%3Aabs

This search only returns the first instance of the abs function, which right now is Simd::<i8, LANES>::abs. The problem here is that abs is implemented for other integers, as well as f32 and f64, making those additional implementations hard to discover. Should perhaps each implementation appear in search? Or should it be easier to find other functions with the same name?