Auto merge of #124401 - oli-obk:some_hir_cleanups, r=cjgillot

Some hir cleanups

It seemed odd to not put `AnonConst` in the arena, compared with the other types that we did put into an arena. This way we can also give it a `Span` without growing a lot of other HIR data structures because of the extra field.

r? compiler

clippy_utils/src/hir_utils.rs

@@ -224,7 +224,7 @@ impl HirEqInterExpr<'_, '_, '_> {
         })
     }
 
-    pub fn eq_array_length(&mut self, left: ArrayLen, right: ArrayLen) -> bool {
+    pub fn eq_array_length(&mut self, left: ArrayLen<'_>, right: ArrayLen<'_>) -> bool {
         match (left, right) {
             (ArrayLen::Infer(..), ArrayLen::Infer(..)) => true,
             (ArrayLen::Body(l_ct), ArrayLen::Body(r_ct)) => self.eq_body(l_ct.body, r_ct.body),
@@ -1116,7 +1116,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
         }
     }
 
-    pub fn hash_array_length(&mut self, length: ArrayLen) {
+    pub fn hash_array_length(&mut self, length: ArrayLen<'_>) {
         match length {
             ArrayLen::Infer(..) => {},
             ArrayLen::Body(anon_const) => self.hash_body(anon_const.body),