[clang] [APINotes][unsafe-buffer-usage] Add [[clang::unsafe_buffer_usage]] support in APINotes (PR #189775)

[Ziqing Luo via cfe-commits]

ziqingluo-90 wrote:

Thanks for reviewing, folks!

@Xazax-hun
I have addressed your comments. Please take another look.
I think when a function is annotated with `[[clang::unsafe_buffer_usage]]` in source, APINotes should have no effect on the attribute.

https://github.com/llvm/llvm-project/pull/189775