Add objc clang format

[qqaatw]

The main PR is #7643. Submitting this PR first to get the CI workflows in the main PR run normally without further approval.

cc @NicolasHug @pmeier.

[pytorch-bot]

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❌ 3 New Failures, 1 Unrelated Failure

As of commit e034624:

NEW FAILURES - The following jobs have failed:

• unittests-linux (3.11, linux.12xlarge, cpu) / linux-job (gh)
• unittests-windows (3.10, windows.4xlarge, cpu) / windows-job (gh)
• windows (windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job (gh)

BROKEN TRUNK - The following job failed but were present on the merge base b9a1984:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• windows (windows.4xlarge, cpu) / windows-job (gh)

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[NicolasHug]

LGTM but the yaml checker is tripping. @pmeier any insight? Maybe we should get rid of it if it's becoming unreliable

[pmeier]

Kinda surprised that it is picking .clang-format as viable target in the first place. I'll have a look.

[pmeier]

According to the clang-format docs:

The .clang-format file uses YAML format:

The hook is configured to trigger on yaml files. The pre-commit docs state

The tags are discovered through a set of heuristics by the identify library. identify was chosen as it is a small portable pure python library.

And indeed

$ identify-cli .clang-format
["file", "non-executable", "text", "yaml"]

In the YAML specification, each --- indicates a separate document. Meaning, here we have two documents in a single file. This is what the hook is complaining about. However, this is not only correct, but also the way to go according to the clang-format documentation.

Thus, we have three options:

1. Ignore .clang-format in the check-yaml hook
2. Add the --allow-multiple-documents option to the hook
3. Disable the hook completely

My preference is 2 > 1 > 3.

[qqaatw]

@NicolasHug @pmeier Thanks. Added the option.

[NicolasHug]

Thanks a lot for the investigation @pmeier . Lint jobs are green so we can merge

[github-actions]

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