设置打印机高度、宽度。传入参数：ai_height (高度) ai_width(宽度)，返回值：以前的打印参数(二进制大对象) 给printsetback()作为参数调用-Set the printer height, width. Incoming parameters: ai_height (height) ai_width (width), the return value: previous print parameters (binary large objects) to print