Function interp_rect_grob 

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

Create a rect grob object without drawing it.

@param x,y center position @param width,height dimensions @param just justification @param gp graphical parameters @param name unique grob name @param vp viewport @return a rect grob object @namespace grid