[clang] [clang-format] Limit how much work guessLanguage() can do (PR #78925)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> Thanks. I've written the clangd patch and posted it for review at #84133.
> 
> If that gets approved, I will abandon this PR.

#84133 has merged now. I'll accordingly close this.

Thank you @owenca for your feedback and helping reach a solution that accomplished the goals of this patch in a claner way!

https://github.com/llvm/llvm-project/pull/78925