Auto merge of #124662 - zetanumbers:needs_async_drop, r=oli-obk

Implement `needs_async_drop` in rustc and optimize async drop glue

This PR expands on #121801 and implements `Ty::needs_async_drop` which works almost exactly the same as `Ty::needs_drop`, which is needed for #123948.

Also made compiler's async drop code to look more like compiler's regular drop code, which enabled me to write an optimization where types which do not use `AsyncDrop` can simply forward async drop glue to `drop_in_place`. This made size of the async block from the [async_drop test](67980dd6fb/tests/ui/async-await/async-drop.rs) to decrease by 12%.

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1560,7 +1560,7 @@ fn confirm_builtin_candidate<'cx, 'tcx>(
         let destructor_def_id = tcx.associated_item_def_ids(trait_def_id)[0];
         assert_eq!(destructor_def_id, item_def_id);
 
-        (self_ty.async_destructor_ty(tcx, obligation.param_env).into(), Vec::new())
+        (self_ty.async_destructor_ty(tcx).into(), Vec::new())
     } else if lang_items.pointee_trait() == Some(trait_def_id) {
         let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);
         assert_eq!(metadata_def_id, item_def_id);