Auto merge of #91230 - eggyal:fallible-type-fold, r=jackh726

Make `TypeFolder::fold_*` return `Result`

Implements rust-lang/compiler-team#432.

Initially this is just a rebase of `@LeSeulArtichaut's` work in #85469 (abandoned; see https://github.com/rust-lang/rust/pull/85485#issuecomment-908781112).  At that time, it caused a regression in performance that required some further exploration... with this rebased PR bors can hopefully report some perf analysis from which we can investigate further (if the regression is indeed still present).

r? `@jackh726` cc `@nikomatsakis`

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2222,6 +2222,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .predicate
             .to_poly_trait_ref()
             .fold_with(&mut self.freshener)
+            .into_ok()
             .with_constness(obligation.predicate.skip_binder().constness);
 
         let dfn = previous_stack.cache.next_dfn();