Polyline Gaps

For #2136.

CC @shunter @mramato 
Also, you can just use the function  in `CesiumMath`.

```javascript
CesiumMath.equalsEpsilonRelativeAndAbsolute(left.x, right.x, absoluteEpsilon, relativeEpsilon) && 
CesiumMath.equalsEpsilonRelativeAndAbsolute(left.y, right.y, absoluteEpsilon, relativeEpsilon)
```