arc.js has a weird rendering artifact over the north pole

In the process of investigating this issue (https://github.com/mapbox/mapbox-gl-js/issues/13121), I discovered some weird rendering artifacts when ``arc.GreatCircle`` draws a line across/near the North Pole:

```html

```

```js
let arcs = [];

let start = { x: -122.375, y: 37.61899948120117};
let end = { x: 55.3643989563, y: 25.2527999878};

var generator = new arc.GreatCircle(start, end);
var line = generator.Arc(100, { offset: 20});
arcs.push(line.json());

map.getSource('LineString').setData({
'type': 'FeatureCollection',
'features': arcs
});
```

Start with the provided arc.js loading snippet and the arc.GreatCircle(...).Arc(100, { offset: 20 }) reproduction. Inspect how the generated line is represented by line.json() and rendered through the LineString source, then verify the north-pole case no longer shows the reported artifact.

Written by the indexing model from the issue text.