`needsCaseBinding` panics instead of being conservative
When the type passed to CoreUtils.needsCaseBinding
(e.g. through MkCore.mkCoreLet
) is levity-polymorphic, GHC panics rather than conservatively assuming that the type might be unlifted.
The simple fix is to use mightBeUnliftedType
instead of isUnliftedType
, MR incoming.