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

[Björn Schäpers via cfe-commits]

HazardyKnusperkeks wrote:

Then I'd go back to `Style.isCpp()`.

What happens if you use libFormat concurrently?

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