GH-46531: [C++] Add type_singleton utility function and tests.

[harshkumar-2005]

Rationale

Introduces a type_singleton(Type::type id) utility to create parameter-free DataType instances
(such as int32, boolean, utf8, etc.) without requiring parameters. Returns an error for
parameterized or unsupported types.

Implementation Details

• Added implementation in type_traits.cc
• Declared function in type_traits.h
• Added comprehensive tests for:
  • Parameter-free types (success cases)
  • Parameterized types (expected error)
  • Invalid type IDs (graceful error handling)

Testing

All tests in arrow-type-test passed locally:

Notes

This utility simplifies internal code where parameter-free type instances are required.

• GitHub Issue: [C++] Add a type_singleton utility function #46531

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[harshkumar-2005]

@pitrou Cl jobs are awaiting maintainer approval. Please approve to trigger the remaining checks.

[harshkumar-2005]

@pitrou
This PR has 9 workflows pending approval. Kindly review and approve to initiate the workflow runs. Thank you!

[github-actions]

⚠️ GitHub issue #46531 has been automatically assigned in GitHub to PR creator.