Better multi-column aggregation support with StringView

[XiangpengHao]

Which issue does this PR close?

Related to #7000. Previous pr was automatically closed because the string-view2 branch is merged.

Rationale for this change

I get some time to implement the multi-column aggregation with StringView, the implementation is inspired by @jayzhan211 's #10976.

However, the performance is mixed, I see almost no performance diff with ClickBench query 18:

SELECT "UserID", extract(minute FROM to_timestamp_seconds("EventTime")) AS m, "SearchPhrase", COUNT(*) FROM hits GROUP BY "UserID", m, "SearchPhrase" ORDER BY COUNT(*) DESC LIMIT 10;

This is becuase the average size of SearchPhrase is only 4, meaning the string is always inlined to view and thus not being reused.

However, I made this query (q14, changed SearchPhrase to URL)

SELECT "SearchEngineID", "URL", COUNT(*) AS c FROM hits WHERE "URL" <> '' GROUP BY "SearchEngineID", "URL" ORDER BY c DESC LIMIT 10;

Without this patch, it takes 7.4s; with this patch, it takes 5.9s, a 20% improvement.

With this patch, the output string will reuse the string values in the buffer, so it is good.
However, when interning the values, we need to hash twice: (1) the string itself to build BytesViewMap (2) the group index - u32, which adds overhead.

What changes are included in this PR?

Things not implemented yet:

• EmtiTo::First(n): I need to think a bit more about how to efficiently reuse the BytesViewBuilder

Are these changes tested?

Are there any user-facing changes?

No