function buffer(extent, value, dest) {
  if (dest) {
    dest[0] = extent[0] - value;
    dest[1] = extent[1] - value;
    dest[2] = extent[2] + value;
    dest[3] = extent[3] + value;
    return dest;
  }
  return [
    extent[0] - value,
    extent[1] - value,
    extent[2] + value,
    extent[3] + value,
  ];
}
Return extent increased by the provided value.
@param {Extent} extent Extent.
@param {number} value The amount by which the extent should be buffered.
@param {Extent} [dest] Extent.
@return {Extent} Extent.
@api