Support changing the styleUrl for vector tiles

[bsvensson]

For "I want to ... Update the URLs of Services in a Web Map", I would like to see support for changing the URL in the styleUrl property of vector tile layers. See webmap spec at https://developers.arcgis.com/web-map-specification/objects/vectorTileLayer/,

e.g.

"baseMap": {
  "baseMapLayers": [
    {
      "id": "VectorTile_3132",
      "type": "VectorTileLayer",
      "layerType": "VectorTileLayer",
      "title": "Dark Blue Canvas",
      "styleUrl": "http://www.arcgis.com/sharing/rest/content/items/8e4423e88139420ca0f0a4edce03523c/resources/styles/root.json",
      "itemId": "8e4423e88139420ca0f0a4edce03523c",
      "visibility": true,
      "opacity": 1
    }
  ],
  "title": "Dark Gray Canvas"
},

item: http://www.arcgis.com/home/webmap/viewer.html?webmap=84bf6b30a1d740fba9f19774e00f0466