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

[Björn Schäpers via cfe-commits]

HazardyKnusperkeks wrote:

> > I mean multiple threads in the same process with different languages. maybe unlikely, but not impossible.
> 
> But libFormat/clang-format are _not_ multithreaded, right?

clang-format is not, but libFormat I don't know. I know my IDE uses directly libFormat.

I will not block this, but I will also not approve it.

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