[C++] Add tests for RandomArrayGenerator

[asfimport]

RandomArrayGenerator is currently untested, and has had some bugs in the past. We should add unit tests for it.

Reporter: Antoine Pitrou / @pitrou

Related issues:

• [C++] Improve configurability of random data generation (is superceded by)

_{Note: This issue was originally created as ARROW-11674. Please see the migration documentation for further details.}

[asfimport]

Todd Farmer / @toddfarmer:
Transitioning issue from Resolved to Closed to based on resolution field value.