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_span/src/symbol.rs

@@ -429,6 +429,7 @@ symbols! {
         async_drop,
         async_drop_chain,
         async_drop_defer,
+        async_drop_deferred_drop_in_place,
         async_drop_either,
         async_drop_fuse,
         async_drop_in_place,