[C++] Support comparing scalars approximately

[asfimport]

As discussed in #7748 (comment) we need to compare scalars approximately in some scenarios. 

Reporter: Liya Fan / @liyafan82
Assignee: Antoine Pitrou / @pitrou

Related issues:

• [C++] arrow::ScalarEquals returns false when values are both null (supercedes)

PRs and other links:

• GitHub Pull Request #8438

_{Note: This issue was originally created as ARROW-10277. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 8438
#8438