Rollup merge of #113661 - oli-obk:tait_wtf, r=lcnr

Double check that hidden types match the expected hidden type

Fixes https://github.com/rust-lang/rust/issues/113278 specifically, but I left a TODO for where we should also add some hardening.

It feels a bit like papering over the issue, but at least this way we don't get unsoundness, but just surprising errors. Errors will be improved and given spans before this PR lands.

r? `@compiler-errors` `@lcnr`

compiler/rustc_trait_selection/src/solve/eval_ctxt.rs

@@ -272,6 +272,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         // assertions against dropping an `InferCtxt` without taking opaques.
         // FIXME: Once we remove support for the old impl we can remove this.
         if input.anchor != DefiningAnchor::Error {
+            // This seems ok, but fragile.
             let _ = infcx.take_opaque_types();
         }