Fix void-arg-adding mechanism for worker/wrapper
As #22725 (closed) shows, in worker/wrapper we must add the void argument
last, not first. See GHC.Core.Opt.WorkWrap.Utils
Note [Worker/wrapper needs to add void arg last]
.
That led me to to study GHC.Core.Opt.SpecConstr
Note [SpecConstr needs to add void args first]
which suggests the
opposite! And indeed I think it's the other way round for SpecConstr
-- or more precisely the void arg must precede the "extra_bndrs".
That led me to some refactoring of GHC.Core.Opt.SpecConstr.calcSpecInfo
.