[clang] [clang-format][NFC] Eliminate the IsCpp parameter in all functions (PR #84599)

[Björn Schäpers via cfe-commits]

HazardyKnusperkeks wrote:

That's okay for clang-format, but you couldn't use libFormat with different languages at once anymore.

I dislike global state in libraries.

https://github.com/llvm/llvm-project/pull/84599