Merge two TupleDescs into one, with td1.numFields + td2.numFields fields, with the first td1.numFields coming from td1 and the remaining from td2. @param td1 The TupleDesc with the first fields of the new TupleDesc @param td2 The TupleDesc with the last fields of the TupleDesc @return the new TupleD
(TupleDesc td1, TupleDesc td2)