ARROW-12728 added a hash_count_distinct hash aggregate kernel, but there is no non-hash count_distinct aggregate kernel.

Reporter: Ian Cook / @ianmcook
Assignee: Percy Camilo Triveño Aucahuasi / @aucahuasi

Related issues:

• [C++][Compute] Implement count_distinct/distinct hash aggregate kernels (relates to)
• [R] Binding for n_distinct() with no grouping (is depended upon by)

PRs and other links:

• GitHub Pull Request #11257

_{Note: This issue was originally created as ARROW-14035. Please see the migration documentation for further details.}