GH-50237: [C++] Migrate arrow/ipc/metadata_internal.h to Result<T>

[Shally-Katariya]

Rationale for this change

Many APIs in arrow/ipc/metadata_internal.h used a T* out parameter
for output and returned a Status. This migrates those APIs to return
Result<T> instead, which is the modern Arrow C++ convention.

What changes are included in this PR?

Migrated the following functions from Status + output parameter pattern
to Result<T>:

• GetKeyValueMetadata
• WriteSchemaMessage
• WriteRecordBatchMessage
• WriteDictionaryMessage

Updated all call sites in:

• arrow/ipc/metadata_internal.cc
• arrow/ipc/reader.cc
• arrow/ipc/message.cc
• arrow/ipc/writer.cc
• arrow/ipc/message_internal_test.cc
• arrow/ipc/read_write_test.cc

Are these changes tested?

Yes. All existing IPC tests pass:

• arrow-ipc-message-internal-test: 8/8 passed
• arrow-ipc-read-write-test: 409/410 passed (1 pre-existing
  failure due to missing ARROW_TEST_DATA)

Are there any user-facing changes?

No. These are internal APIs so no compatibility changes are needed.

Closes #50237

• GitHub Issue: [C++] Migrate arrow/ipc/metadata_internal.h to Result<T> #50237

[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

[Reranko05]

I can see some formatting issues in the diff. Could you run: python -m pre_commit run clang-format --files <modified_files> locally and push the resulting changes?

[Shally-Katariya]

@Reranko05 formatting fixed

[pitrou]

Thanks @Shally-Katariya ! This is looking mostly good, just one suggestion below.

[pitrou]

This declaration is unused now, right? Let's just remove it?

[Shally-Katariya]

Done

[pitrou]

+1, thank you @Shally-Katariya . Let's wait for CI.