Bug #29660945: SIG 6 AT TEMPTABLE::HANDLER::POSITION | SRC/HANDLER.CC

There are certain cases where we currently materialize, but don't need to:

 - If doing a sort at the end of a join (e.g. for grouping), and we don't sort
   by row IDs, we can just stream the data directly from the correct iterator
   into the SortingIterator. (This is now possible to know, since after the fix
   for #29595346, we know when creating the SortingIterator whether it will be by
   row IDs or not.)
 - If materializing a derived table that we don't intend to read from multiple
   times, and would only table scan.

Fix both cases by means of a new StreamingIterator that does the required
copying of fields and nothing else.

Note that since we now decide ahead-of-time whether we want to sort by row IDs
or not, we have somewhat less information; we don't necessarily know the number
of rows to sort (used for priority queue decisions), and there are a few cases
where it would be slightly better to sort by row ID that we now do not.
The benefits from the more common cases should be more than enough to offset
this.

Re-submit with fix for #29660945: Stop stripping off addon fields at sorting
time to get a bigger chance of using the priority queue.

Change-Id: I5f187ed60d1b974b940c5dc614fe9b0bb3a87d51