Function interp_circle_grob 

fn interp_circle_grob(
    args: &[RValue],
    named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Create a circle grob object without drawing it.

@param x,y center position @param r radius @param gp graphical parameters @param name unique grob name @param vp viewport @return a circle grob object @namespace grid