addLayer(layer) {
    const layers = this.getLayerGroup().getLayers();
    layers.push(layer);
  }
Adds the given layer to the top of this map. If you want to add a layer
elsewhere in the stack, use `getLayers()` and the methods available on
{@link module:ol/Collection~Collection}.
@param {import("./layer/Base.js").default} layer Layer.
@api