Auto merge of #71049 - eddyb:const-err, r=oli-obk

Auto merge of #71049 - eddyb:const-err, r=oli-obk

Add `ConstKind::Error` and convert `ErrorHandled::Reported` to it.

By replicating the `ty::Error` approach to encoding "an error has occurred", all of the mechanisms that skip redundant/downstream errors are engaged and help out (see the reduction in test output).

This PR also adds `ErrorHandled::Linted` for the lint case because using `ErrorHandled::Reported` *without* having emitted an error that is *guaranteed* to stop compilation, is incorrect now.

r? @oli-obk cc @rust-lang/wg-const-eval @varkor @yodaldevoid