Show a control point for the center of a spiral
Spirals in Inkscape define a center point but the user cannot easily control the position of the center.
Show a control point for the center so it's easier to move the shape around and snap it by its center.
This was discussed also in https://gitlab.com/ao2/inkscape/commit/ead3bb1180863f94657892014c7839b994eaacdd