[clang] [clang] Apply internal buffering to clang diagnostics printing (PR #113440)

[Mariya Podchishchaeva via cfe-commits]

Fznamznon wrote:

> I'm also a bit worried we're updating TextDiagnostic but not SARIFDiagnostic; does emitting to SARIF also have interleaving issues?

It seems it does
<img width="1279" alt="image" src="https://github.com/user-attachments/assets/2837334a-891f-4e1b-8fd0-2f456745ada0">

I'll try to see what happens in raw_ostream.

https://github.com/llvm/llvm-project/pull/113440