Rollup merge of #99401 - TaKO8Ki:avoid-symbol-to-&str-conversions, r=nnethercote

Avoid `Symbol` to `&str` conversions

`Symbol::as_str` is a slowish operation, so this patch removes some usages of it.

compiler/rustc_resolve/src/diagnostics.rs

@@ -1627,7 +1627,7 @@ impl<'a> Resolver<'a> {
                     "{}{} `{}` defined here",
                     prefix,
                     suggestion.res.descr(),
-                    suggestion.candidate.as_str(),
+                    suggestion.candidate,
                 ),
             );
         }