GH-47207: [C++][C++23] Upgrade Arrow to be compatible with C++23 rebase-47318

[BwL1289]

Rationale for this change

Arrow’s C++ codebase currently targets an older C++ standard. Moving to C++23 helps keep the project aligned with modern compiler defaults, enables new language features, and ensures continued compatibility with upcoming compiler versions.

During this upgrade, several forward declaration patterns used in the codebase became invalid under C++23 rules, requiring changes to maintain build correctness.

What changes are included in this PR?

This PR updates code to resolve forward declaration errors triggered by C++23 compliance checks. Specifically, it corrects invalid or outdated forward declarations that are rejected by C++23.

Applies the fixes in:

• cpp/src/arrow/acero/asof_join_node.cc
• cpp/src/arrow/filesystem/mockfs.cc
• cpp/src/arrow/flight/types.h

Are these changes tested?

Yes.

Are there any user-facing changes?

No.

• GitHub Issue: [C++] c++23 supported? #47207
• Rebased GH-47317: [C++][C++23][Gandiva] Use pointer for Cache test #47318

[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

[BwL1289]

@kou @lidavidm the rebased PR is here

[BwL1289]

@kou bumping this

[kou]

Could you use git rebase not git merge to avoid including needless changes such as https://github.com/apache/arrow/pull/47415/files#diff-a8a50af24f976aca78d9169c24e3c2f43c2b722b96769d4b0c6f19e65189e8ea ?

[BwL1289]

This is rebased.

[kou]

Could you share the command lines you used? It seems that the rebase target branch was wrong.

Anyway, there are many CI failures. We can't accept this change.

[BwL1289]

Ok, I'm just going to close this then.

[BwL1289]

FWIW, your comment: #47328 (comment)

git fetch https://github.com/apache/arrow pull/47318/head:pr-47318
git rebase pr-47318

[kou]

You need to rebase on https://github.com/apache/arrow/tree/main not pull/47318/head.