GH-15192: [C++] Bring back case_when tests for union types

[zanmato1984]

Rationale for this change

Bring back the problematic test case of random case_when on union(bool, string) type. This case used to fail. However #36018 already addressed the issue.

More information about how it used to fail, please refer to #15192 (comment).

What changes are included in this PR?

Bring back the test code.

Are these changes tested?

Yes, the change is the test.

Are there any user-facing changes?

No.

• Closes: [C++] "case_when" test failure on random union inputs #15192

[github-actions]

⚠️ GitHub issue #15192 has been automatically assigned in GitHub to PR creator.

[pitrou]

@github-actions crossbow submit -g cpp

[pitrou]

+1, thank you @zanmato1984 !

[github-actions]

Revision: c27166f

Submitted crossbow builds: ursacomputing/crossbow @ actions-ede34c36c9

Task	Status
test-alpine-linux-cpp
test-build-cpp-fuzz
test-conda-cpp
test-conda-cpp-valgrind
test-cuda-cpp
test-debian-11-cpp-amd64
test-debian-11-cpp-i386
test-fedora-38-cpp
test-ubuntu-20.04-cpp
test-ubuntu-20.04-cpp-bundled
test-ubuntu-20.04-cpp-minimal-with-formats
test-ubuntu-20.04-cpp-thread-sanitizer
test-ubuntu-22.04-cpp
test-ubuntu-22.04-cpp-20
test-ubuntu-22.04-cpp-no-threading

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 6 benchmarking runs that have been run so far on merge-commit 2308cdf.

There was 1 benchmark result indicating a performance regression:

• Commit Run on ursa-i9-9960x at 2023-12-21 10:55:51Z
  • tpch (R) with engine=arrow, format=native, language=R, memory_map=False, query_id=TPCH-08, scale_factor=1

The full Conbench report has more details. It also includes information about 1 possible false positive for unstable benchmarks that are known to sometimes produce them.