[C++] Add unit tests and documentation for swiss-join

[asfimport]

The swiss join utilities being added as part of ARROW-14182 are not adequately unit tested at the moment. They have fairly decent coverage from end-to-end random hash join testing. However, a set of basic unit tests will help future maintenance by demonstrating basic usage and allowing for more targeted fixes when a refactor breaks something. I'm doing some of this work as I review ARROW-14182 anyways so that I can better understand it. Rather than complicate the review I will open this as a separate follow-up PR.

Reporter: Weston Pace / @westonpace

PRs and other links:

• GitHub Pull Request #13751

_{Note: This issue was originally created as ARROW-17022. Please see the migration documentation for further details.}

[asfimport]

Apache Arrow JIRA Bot:
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[github-actions]

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