Auto merge of #90737 - eholk:intofuture, r=tmandry

Reintroduce `into_future` in `.await` desugaring

This is a reintroduction of the remaining parts from https://github.com/rust-lang/rust/pull/65244 that have not been relanded yet.

This isn't quite ready to merge yet. The last attempt was reverting due to performance regressions, so we need to make sure this does not introduce those issues again.

Issues #67644, #67982

/cc `@yoshuawuyts`

compiler/rustc_span/src/symbol.rs

@@ -196,6 +196,7 @@ symbols! {
         Implied,
         Input,
         Into,
+        IntoFuture,
         IntoIterator,
         IoRead,
         IoWrite,
@@ -737,6 +738,7 @@ symbols! {
         inout,
         instruction_set,
         intel,
+        into_future,
         into_iter,
         intra_doc_pointers,
         intrinsics,