function addTileRepresentationToLookup(
  tileRepresentationLookup,
  tileRepresentation,
  z,
) {
  const representationsByZ = tileRepresentationLookup.representationsByZ;
  if (!(z in representationsByZ)) {
    representationsByZ[z] = new Set();
  }
  representationsByZ[z].add(tileRepresentation);
  tileRepresentationLookup.tileIds.add(getUid(tileRepresentation.tile));
}
Add a tile representation to the lookup.
@param {TileRepresentationLookup} tileRepresentationLookup Lookup of tile representations by zoom level.
@param {AbstractTileRepresentation} tileRepresentation A tile representation.
@param {number} z The zoom level.