Waypoint style

Nobody has claimed this yet.

Can't see waypoints on map, even while overriding style.
```
var mapDirections = new MapboxDirections({ // eslint-disable-line no-undef
accessToken: mapboxgl.accessToken, // eslint-disable-line no-undef
unit: 'metric',
profile: 'mapbox/cycling',
interactive: false,
controls: {
inputs: false,
instructions: false,
profileSwitcher: false,
},
styles: [
{
'id': 'directions-waypoint-point',
'type': 'circle',
'source': 'directions',
'paint': {
'circle-radius': 60,
'circle-color': '#fa8bc9',
},
'filter': [
'all',
['in', '$type', 'Point'],
['in', 'id', 'waypoint'],
],
}
],
})
```

Start from the MapboxDirections configuration and its styles array, reproducing the reported case with interactive and controls disabled. Verify how the directions waypoint layer is rendered and why the supplied circle style does not make it visible; done means waypoints appear with the requested styling on the map.

Written by the indexing model from the issue text.