GH-49872: [C++] Remove deprecated std::is_trivial

[fdr400]

Resolves #49872

Rationale for this change

std::is_trivial is deprecated since C++26, so it leads to warning when building app with Apache Arrow and new C++ standard

What changes are included in this PR?

This PR applies suggestion from libc++ code: 'is_trivial<std::shared_ptr<arrow::io::ReadableFile>>' is deprecated: Consider using is_trivially_copyable<T>::value && is_trivially_default_constructible<T>::value instead

Are these changes tested?

Tested with CI

Are there any user-facing changes?

Changes allow user to build with warning as error flags

• GitHub Issue: [C++] remove deprecated is std::is_trivial #49872

[github-actions]

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[github-actions]

⚠️ GitHub issue #49872 has been automatically assigned in GitHub to PR creator.

[fdr400]

@pitrou hello! I am believe my contribution did not effect the failed Python CI job. But it seems that C++ Extra workflows was skipped because of that
Maybe we should rerun the CI?

[pitrou]

I think the C++ Extra builds actually ran fine. Two of them were skipped for unrelated reasons.

And you're right that the macOS Python build failure looks unrelated.

[pitrou]

LGTM, thank you @fdr400