`span_suggestions` is to provide mutually exclusive suggestions. When it was introduced, we made its behavior be that if a single suggestion is given to it, we present the suggestion inline, otherwise in patch format. Changing this to make all of its uses be verbose, as that is closer in intent of output.
Get rid of HIR const checker
As far as I can tell, the HIR const checker was implemented in https://github.com/rust-lang/rust/pull/66170 because we were not able to issue useful const error messages in the MIR const checker.
This seems to have changed in the last 5 years, probably due to work like #90532. I've tweaked the diagnostics slightly and think the error messages have gotten *better* in fact.
Thus I think the HIR const checker has reached the end of its usefulness, and we can retire it.
cc `@RalfJung`