public Feature setNumPointsAttr(String numPointsAttr) {
      this.numPointsAttr = numPointsAttr;
      return this;
    }
Sets a special attribute key that the renderer will use to store the number of points in the simplified geometry
before slicing it into tiles.
planetiler-core/src/main/java/com/onthegomap/planetiler/FeatureCollector.java