Sort options for DataType::Dictionary is incorrect

[mingmwang]

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Looks like when the DataType is Dictionary, it always reset the Nulls First settings and ignore the sort option from the query engine. This will generate wrong sort result. I will add a UT to reproduce the issue.

https://github.com/apache/arrow-rs/blob/a0a5880665b1836890f6843b6b8772d81c463351/arrow-ord/src/sort.rs#L316-L332

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[tustvold]

The logic you link to is fairly well tested - https://github.com/apache/arrow-rs/blob/a0a5880665b1836890f6843b6b8772d81c463351/arrow-ord/src/sort.rs#L2998

There is, however, a known issue with lexsort's handling of nested nulls in dictionaries - apache/arrow-rs#2687 although again it should be noted that arrow-rs will not generate such arrays naturally.