[C++] Add nulls position option to sort functions

[asfimport]

Currently in the sort functions, nulls are considered greater than any other value and are sorted at the the end of the array. Add an option to enable users to sort nulls at the beginning if they wish. This option is common in analytic data systems, e.g. SQL NULLS FIRST and NULLS LAST, pandas na_position, R na.last.

Reporter: Ian Cook / @ianmcook
Assignee: Antoine Pitrou / @pitrou

Related issues:

• [C++] Add ChunkedArray::GetScalar (supercedes)
• [R] Expose null placement option through sort bindings (is depended upon by)

PRs and other links:

• GitHub Pull Request #11212

_{Note: This issue was originally created as ARROW-12063. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
This is probably desirable, and will also be slightly delicate to implement (there's a lot of sorting code already).

(Note it's not only nulls but also NaNs...)

[asfimport]

David Li / @lidavidm:
Issue resolved by pull request 11212
#11212