Dissect an arc into its core properties.

Input parameters:

1. Ar → Arc to dissect.

Output parameters:

1. Pl → Base plane representing both the centre and the orientation of the arc.
2. Rd → Radius of the arc.
3. As → Angle of the start of the arc, as measured anti-clockwise from the arc plane x-axis.
4. Aw → Angle of the interior of the arc, as measured anti-clockwise within the arc plane.