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

[Owen Pan via cfe-commits]

owenca wrote:

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

That would still require passing `Style.isCpp()` as the parameter to the `FormatToken` (and other) functions.

> What happens if you use libFormat concurrently?

Can you elaborate? Doesn't each process get its own copy of the globals of a shared library?

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