* [feature](planner): push limit to olapscan when meet sort.
* if olap_scan_node's sort_info is set, push sort_limit, read_orderby_key
and read_orderby_key_reverse for olap scanner
* There is a common query pattern to find latest time serials data.
eg. SELECT * from t_log WHERE t>t1 AND t<t2 ORDER BY t DESC LIMIT 100
If the ORDER BY columns is the prefix of the sort key of table, it can
be greatly optimized to read much fewer data instead of read all data
between t1 and t2.
By leveraging the same order of ORDER BY columns and sort key of table,
just read the LIMIT N rows for each related segment and merge N rows.
1. set read_orderby_key to true for read_params and _reader_context
if olap_scan_node's sort info is set.
2. set read_orderby_key_reverse to true for read_params and _reader_context
if is_asc_order is false.
3. rowset reader force merge read segments if read_orderby_key is true.
4. block reader and tablet reader force merge read rowsets if read_orderby_key is true.
5. for ORDER BY DESC, read and compare in reverse order
5.1 segment iterator read backward using a new BackwardBitmapRangeIterator and
reverse the result block before return to caller.
5.2 VCollectIterator::LevelIteratorComparator, VMergeIteratorContext return
opposite result for _is_reverse order in its compare function.
Co-authored-by: jackwener <jakevingoo@gmail.com>
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