Make axis-ordering generic

Use `axis_order` rather than hard-coded `xyz`, so that datasets with ordering such as `zyx` may be supported.

Co-authored-by: Chris Havlin <[email protected]>

yt/visualization/volume_rendering/off_axis_projection.py

@@ -450,7 +450,7 @@ def temp_weightfield(field, data):
         )
 
         for idim, periodic in enumerate(data_source.ds.periodicity):
-            axis = "xyz"[idim]
+            axis = data_source.ds.coordinates.axis_order[idim]
             xyz[..., idim] = data_source["index", axis] - center[idim]
             if not periodic:
                 continue