[clang] [clang-tools-extra] [llvm] [clang-format] Add support for BasedOnStyle referencing an arbitrary file (PR #107312)

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mydeveloperday wrote:

> You are touching a lot of projects. I don't know how others feel about that, but my preference would be to tackle one project per PR.

+1

https://github.com/llvm/llvm-project/pull/107312