flatten should be single-step, not recursive

[findepi]

Describe the bug

per #13706 the list functions are modeled after DuckDB¹

per https://duckdb.org/docs/sql/functions/list.html#flattenlist_of_lists, flatten should flatten one level, not recursive

To Reproduce

query ???
select flatten(arrow_cast(make_array([[1.1]], [[2.2]], [[3.3], [4.4]]), 'LargeList(LargeList(LargeList(Float64)))'));
----
[1.1, 2.2, 3.3, 4.4]

Expected behavior

query ???
select flatten(arrow_cast(make_array([[1.1]], [[2.2]], [[3.3], [4.4]]), 'LargeList(LargeList(LargeList(Float64)))'));
----
[[1.1], [2.2], [3.3], [4.4]]

Additional context

No response

Footnotes

1. i would prefer a more established point of reference with close alignment to the SQL standard, but this issue is not about this ↩

[buraksenn]

I want to work on this but saw a related work in the #13756 should I wait or simply convert flattern func to flatten one level instead of recursion?

[findepi]

You don't need to wait, but you can. We should expect some conflicts, someone will have to resolve.