[clang] [clang-format]: Add `Custom` to `ShortFunctionStyle`; add new AllowShortFunctionsOnASingleLineOptions for granular setup (PR #134337)

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irymarchyk wrote:

If this was done previously I think this is doable. I will take a look and make appropriate changes. Thanks.

https://github.com/llvm/llvm-project/pull/134337