REF: share to_native_types with ArrayManager
also combine implementations of Block.fill_value
@jorisvandenbossche are you happy with this approach?  if so, i think can use it to get rid of at least one or two more uses of apply_with_block > Should we try to find a better place to put the to_native_types function?

Sure.  Have somewhere in mind? Not directly a better idea. Let's worry about that later.