Rollup merge of #147171 - Qelxiros:hashmap_diag, r=fee1-dead

recommend using a HashMap if a HashSet's second generic parameter doesn't implement BuildHasher

closes rust-lang/rust#147147

~The suggestion span is wrong, but I'm not sure how to find the right one.~ fixed

I'm relatively new to the diagnostics ecosystem, so I'm not sure if `span_help` is the right choice. `span_suggestion_*` might be better, but the output from `x test` looks weird in that case.

Author: matthiaskrgr