[Subtask]: Rollup using Sort

### Parent Issue

#20650

### Detail of Subtask

select c1, c2, avg(x) from T group by roll up (c1, c2);

The query plan should be Scan T -> Order by C1, C2 -> Rollup Agg

select

### Describe implementation you've considered

_No response_

### Additional information

_No response_