Labels/billboards/points crossing the IDL in 2D get clipped


Models are OK across the IDL, #3764.

```js
var viewer = new Cesium.Viewer('cesiumContainer', {
sceneMode : Cesium.SceneMode.SCENE2D
});

viewer.entities.add({
position : Cesium.Cartesian3.fromDegrees(175, 40.03883),
billboard :{
image : '../images/Cesium_Logo_overlay.png'
}
});
```

Start by running the provided Cesium.Viewer SCENE2D reproduction with the entity at 175 degrees longitude and inspect the billboard rendering around the international date line. Compare the behavior with the referenced model issue #3764. Done means labels, billboards, and points crossing the IDL render without being clipped in 2D.

Written by the indexing model from the issue text.