Check for overflow in assemble_candidates_after_normalizing_self_ty
          #109683
        
          
      
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Prevents a stack overflow (:warning: :exclamation:) in the new solver when we have param-env candidates that look like:
T: Trait<Assoc = <T as Trait>::Assoc>The current error message looks bad, but that's because we don't distinguish overflow and other ambiguity errors. I'll break that out into a separate PR since the fix may be controversial.
r? @lcnr