Add some additional tests and comments in response to comments on #10190

Reporter: Ian Cook / @ianmcook
Assignee: Ian Cook / @ianmcook

Related issues:

• [R] Bindings for strsplit (depends upon)

PRs and other links:

• GitHub Pull Request #10271

_{Note: This issue was originally created as ARROW-12692. Please see the migration documentation for further details.}