default void write(ByteBuffer buf, int offset) {
    KeyValueUtil.appendTo(this, buf, offset, true);
  }
Write this Cell into the given buf's offset in a {@link KeyValue} format.
@param buf    The buffer where to write the Cell.
@param offset The offset within buffer, to write the Cell.
hbase-common/src/main/java/org/apache/hadoop/hbase/ExtendedCell.java