[clang] Respect the [[clang::unsafe_buffer_usage]] attribute for field and constructor initializers (PR #91991)

[Dana Jansens via cfe-commits]

danakj wrote:

Sorry I just haven't gotten back to making the fixes yet. If someone else wants to apply them and land it I won't be upset, otherwise I will get to this eventually..

https://github.com/llvm/llvm-project/pull/91991