[clang] [analyzer][NFC] Take BugReport descriptions as Twine instead of StringRef (PR #205527)

[Balázs Benics via cfe-commits]

steakhal wrote:

I also forgot to clean up the includes, addressed in https://github.com/llvm/llvm-project/pull/205527/commits/d99e56a4f5f48bfb28209ae750786338f45e046d.

https://github.com/llvm/llvm-project/pull/205527