[clang-tools-extra] [clang-tidy] Add modernize-default-arg-braced-init check (PR #203474)

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AntonyCJ30 wrote:

"I understand the policy. I haven't enabled Copilot review comments myself - this appears to be either a GitHub default feature or was triggered by someone else. I'll check my GitHub settings to disable it. Thank you for letting me know."

https://github.com/llvm/llvm-project/pull/203474