Preprocessor update

[twelch]

• update preprocessing functions
  • drop use of clipToPolygonFeatures and use lower level code instead
  • add biggestPolygon helper function
  • directly use subdivided flatgeobuf global datasources instead of VectorDataSource bundles. no need to register them in datasources.json just directly use URL.
  • switch from osm land to Daylight coastline polygons
  • clipToLand - fix bug where if land feature fetch returned no polygons it would return the original sketch, instead of throwing that the sketch is outside the land boundary.
• refine polygonSmokeTest logging
• re-export toJsonFile helper