Auto merge of #77873 - sexxi-goose:use_tuple_inference_for_closures, r=nikomatsakis

Replace tuple of infer vars for upvar_tys with single infer var

This commit allows us to decide the number of captures required after
completing capture ananysis, which is required as part of implementing
RFC-2229.

closes https://github.com/rust-lang/project-rfc-2229/issues/4
r? `@nikomatsakis`

compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs

@@ -110,7 +110,7 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
         // check if *any* of those are trivial.
         ty::Tuple(ref tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t.expect_ty())),
         ty::Closure(_, ref substs) => {
-            substs.as_closure().upvar_tys().all(|t| trivial_dropck_outlives(tcx, t))
+            trivial_dropck_outlives(tcx, substs.as_closure().tupled_upvars_ty())
         }
 
         ty::Adt(def, _) => {