We're now supporting using stale TileJSON and GeoJSON data. When we receive a new answer with an updated TileJSON file, we're replacing the Source's metadata with the new one and trigger updates to make sure we're loading the correct tiles. Similarly, GeoJSON data will be reparsed.
This adds support for using cached styles that are stale. They're treated like changing styles; when the refreshed style changed compared to the one we've already had, we're swapping out the entire style, which might cause a slight flicker.
