mill_raster_2D doesn't guarantee inside-out ordering

The mill_raster_2D module used to give an inside-out path order when you turn off distance sort and select the "reverse" path order. This is important for milling shapes with internal cutouts (vias, bolt holes, internal features, etc.) because if you mill the outside path first, the part is freed (or only held by a small amount of double sided tape). Mostly this is fine, but it causes any critical dimensions to be off (and can occasionally be catastrophic to the job).

Here is a file that I can't get mill_raster_2D to give an inside-out path ordering for: https://gitlab.cba.mit.edu/calischs/step/blob/72a9f3030bf49428b4fe0fcd754d39693b8782a4/nrf52-stepper/nrf52-stepper-interior.png