xform: minimize number of temporaries when destructuring `skip_state`
xform: minimize number of temporaries when destructuring `skip_state`

This is because:

- We don't need to use `otherwise<>` (which would copy the lambda in it)
  because the new return type deduction rules don't need it.

- We replace `std::bind` with more light-weight constructs for our
  specific cases that perfect-forward the bound arguments.

shaunstanislaus/atria,respu/atria,AbletonAG/atria,Ableton/atria,respu/atria,bowlofstew/atria,lyrl/atria,lyrl/atria,iankronquist/atria,manashmndl/atria,AbletonAG/atria,bowlofstew/atria,Ableton/atria,respu/atria,dodheim/atria,manashmndl/atria,AbletonAG/atria,kod3r/atria,manashmndl/atria,dodheim/atria,iankronquist/atria,iankronquist/atria,kod3r/atria,bowlofstew/atria,shaunstanislaus/atria,kod3r/atria,lyrl/atria,shaunstanislaus/atria,Ableton/atria,dodheim/atria