Rollup merge of #114351 - ttsugriy:sort-by-words, r=fee1-dead

[rustc_span][perf] Remove unnecessary string joins and allocs.

Comparing vectors of string parts yields the same result but avoids unnecessary `join` and potential allocation for resulting `String`. This code is cold so it's unlikely to have any measurable impact, but considering but since it's also simpler, why not? :)

Author: matthiaskrgr