Auto merge of #51316 - oli-obk:const_err, r=nikomatsakis

Auto merge of #51316 - oli-obk:const_err, r=nikomatsakis

Refactor the const eval diagnostic API

* no longer report "const eval error" for things that have typeck errors
* errors and lints have saner spans and messages
* unified the diagnostic logic (const eval errors were slightly different depending on where they were reported, and there was also code duplication between the different reporters)
* report errors if an erroneous constant is used inside a promoted (fixes most of #50814)