function gatherContentHeaders(tileJson) {
  if (hasExtension(tileJson, "3DTILES_multiple_contents")) {
    const extension = tileJson.extensions["3DTILES_multiple_contents"];
    return defined(extension.contents) ? extension.contents : extension.content;
  }

  if (defined(tileJson.contents)) {
    return tileJson.contents;
  }

  if (defined(tileJson.content)) {
    return [tileJson.content];
  }

  return [];
}
Gather JSON headers for all contents in the tile.
This handles both regular tiles and tiles with multiple contents, either
in the contents array (3D Tiles 1.1) or the `3DTILES_multiple_contents` extension

@param {object} tileJson The JSON header of the tile with either implicit tiling (3D Tiles 1.1) or the 3DTILES_implicit_tiling extension.
@return {Object[]} An array of JSON headers for the contents of each tile
@private