[clang] [clang] clang-format functionality related to format string parsing (NFC) (PR #195644)

[Sergei Barannikov via cfe-commits]

s-barannikov wrote:

Note that this touches more than strictly necessary. I'm doing some changes downstream in the same area, and keeping files formatted helps reduce downstream diffs too.


https://github.com/llvm/llvm-project/pull/195644