Auto merge of #121018 - oli-obk:impl_unsafety, r=TaKO8Ki

Fully stop using the HIR in trait impl checks

At least I hope I found all happy path usages. I'll need to check if I can figure out a way to make queries declare that they don't access the HIR except in error paths

compiler/rustc_middle/src/ty/mod.rs

@@ -252,6 +252,7 @@ pub struct ImplHeader<'tcx> {
 pub struct ImplTraitHeader<'tcx> {
     pub trait_ref: ty::TraitRef<'tcx>,
     pub polarity: ImplPolarity,
+    pub unsafety: hir::Unsafety,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, TypeFoldable, TypeVisitable)]