1. remove forcing nullable for slot on EmptySetNode.
2. order by xxx desc should use nulls last as default order.
3. don't create runtime filter if runtime filter mode is OFF.
4. group by constant value need check the corresponding expr shouldn't have any aggregation functions.
5. fix two left outer join reorder bug( A left join B left join C).
6. fix semi join and left outer join reorder bug.( A left join B semi join C ).
7. fix group by NULL bug.
8. change ceil and floor function to correct signature.
9. add literal comparasion for string and date type.
10. fix the getOnClauseUsedSlots method may not return valid value.
11. the tightness common type of string and date should be date.
12. the nullability of set operation node's result exprs is not set correctly.
13. Sort node should remove redundent ordering exprs.
support distinct count with group by clause.
for example:
SELECT count(distinct c_custkey + 1) FROM customer group by c_nation;
TODO: support distinct count without group by clause.
