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.

Issues GH-67644, GH-67982

compiler/rustc_ast_lowering/src/lib.rs

@@ -162,6 +162,7 @@ struct LoweringContext<'a, 'hir: 'a> {
 
     allow_try_trait: Option<Lrc<[Symbol]>>,
     allow_gen_future: Option<Lrc<[Symbol]>>,
+    allow_into_future: Option<Lrc<[Symbol]>>,
 }
 
 pub trait ResolverAstLowering {
@@ -320,6 +321,7 @@ pub fn lower_crate<'a, 'hir>(
         in_scope_lifetimes: Vec::new(),
         allow_try_trait: Some([sym::try_trait_v2][..].into()),
         allow_gen_future: Some([sym::gen_future][..].into()),
+        allow_into_future: Some([sym::into_future][..].into()),
     }
     .lower_crate(krate)
 }