Support aggregate function as OVER window function

[xxchan]

e.g., nexmark Q6

SELECT
    Q.seller,
    AVG(Q.final) OVER
        (PARTITION BY Q.seller ORDER BY Q.date_time ROWS BETWEEN 10 PRECEDING AND CURRENT ROW)
    as avg
FROM (
    SELECT MAX(B.price) AS final, A.seller, B.date_time
    FROM auction AS A, bid AS B
    WHERE A.id = B.auction and B.date_time between A.date_time and A.expires
    GROUP BY A.id, A.seller
) AS Q;

To support Grouping TopN #4847, we will first support special window functions row_numer() (or rank(), dense_rank()) only.

[github-actions]

This issue has been open for 60 days with no activity. Could you please update the status? Feel free to continue discussion or close as not planned.

[xxchan]

risingwavelabs/rfcs#8

[stdrc]

With #9110, #9248 and #9597 I guess we now support aggregating over window, though only for Emit-On-Window-Close mode. I'm closing this issue now, cuz later general version of over window executor is not really related to aggregate over window support.