[C++][Compute] Add variance kernel benchmark

[asfimport]

Reporter: Yibo Cai / @cyb70289
Assignee: Yibo Cai / @cyb70289

PRs and other links:

• GitHub Pull Request #8407

_{Note: This issue was originally created as ARROW-10241. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 8407
#8407