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

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irymarchyk wrote:

> We should stick to the table in [#134337 (comment)](https://github.com/llvm/llvm-project/pull/134337#discussion_r2028339995) and deprecate `SFS_InlineOnly`, `SFS_Empty`, and `SFS_Inline`.

Thanks, I marked options as 'deprecated'. Mapping is done in Format.cpp.

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