Check that RPITs are compatible with the opaques inferred during HIR typeck too

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -155,10 +155,6 @@ pub struct TypeckResults<'tcx> {
     /// We also store the type here, so that the compiler can use it as a hint
     /// for figuring out hidden types, even if they are only set in dead code
     /// (which doesn't show up in MIR).
-    ///
-    /// These types are mapped back to the opaque's identity substitutions
-    /// (with erased regions), which is why we don't associated substs with any
-    /// of these usages.
     pub concrete_opaque_types: FxIndexMap<ty::OpaqueTypeKey<'tcx>, ty::OpaqueHiddenType<'tcx>>,
 
     /// Tracks the minimum captures required for a closure;