Add new setting to specify 2D point shape in vtkProperty

You can now draw round points by calling the new vtkProperty::SetPoint2DShape() method with a value of vtkProperty::Point2DShapeType::Round. The default value is vtkProperty::Point2DShapeType::Square. Note that points will be rendered as spheres when RenderPointsAsSpheres is turned on irrespective of the value of Point2DShape.

This feature is only implemented in the new WebGPU rendering module. The OpenGL module ignores this setting.