set line width in metal

There is no way to control line width in the same way as a [point size](https://github.com/cocos2d/cocos2d-x/issues/19763) in Metal. 
An option would be to draw the line as a quad (a box). Or you can program a  line thickness shader as described [here](https://stackoverflow.com/questions/15276454/is-it-possible-to-draw-line-thickness-in-a-fragment-shader)
