this implementation is hoped to be smaller. (feather_m4_express/fr fits
unlike the other PR; approximate savings ~600 bytes)
Minor difference to standard Python: A `dict` object has a
`move_to_end` method. However, calling this method always results in
TypeError.
Implementing it this way means that the method table can still be shared
between OrderedDict and builtin dict.
Closes#4408.
Jeff Epler