Two of the handles permit changing the angles of the sector; one handle permits changing the radius of the sector.

Note that the Geometry returned by `makeSector` always returns a Geometry that occupies the area that would be occupied by a full circle. That Geometry-creating function also depends on three data properties, `radius`, `angle`, and `sweep`.

This extension tool is defined in its own file, as SectorReshapingTool.ts.