wrong geometry output from query*Features for MultiPoint and Polygon/MultiPolygon features

[jfirebaugh]

vectortile_to_geojson.js has several bugs that prevent it from returning the correct GeoJSON geometry for MultiPoint, Polygon, and MultiPolygon features:

• It inherits this bug from code copied from vector-tile-js. (Not sure why this code was copied rather than using VectorTileFeature#toGeoJSON. @ansis?)
• It doesn't use classifyRings, so it can't tell the difference between Polygons with inner rings and MultiPolygons. Note that Normalize geometry structure; classify polygon rings vector-tile-js#33 proposes to bring classifyRings into vector-tile-js, which would allow us to use VectorTileFeature#toGeoJSON for this as well.

[jfirebaugh]

#2294

[jfirebaugh]

Blocked by mapbox/vector-tile-js#45.