Teach typeck/borrowck/solvers how to deal with async closures

compiler/rustc_middle/src/query/mod.rs

@@ -755,6 +755,11 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    query coroutine_for_closure(def_id: DefId) -> DefId {
+        desc { |_tcx| "TODO" }
+        separate_provide_extern
+    }
+
     /// Gets a map with the variance of every item; use `variances_of` instead.
     query crate_variances(_: ()) -> &'tcx ty::CrateVariancesMap<'tcx> {
         arena_cache