[clang] [analyzer][docs] Update the release notes for llvm-18 (PR #76446)

[Balazs Benics via cfe-commits]

steakhal wrote:

The `docs-clang-html` build target produces the following html document at `tools/clang/docs/html/ReleaseNotes.html#static-analyzer`, without any warnings:
![image](https://github.com/llvm/llvm-project/assets/6280485/3c90c648-ba56-476d-8ba2-0e1d2ba8402a)

https://github.com/llvm/llvm-project/pull/76446