[clang] [SSAF][UnsafeBufferUsage] Add APIs to the EntityPointerLevel module for UnsafeBufferUsage (PR #191333)

[Balázs Benics via cfe-commits]

https://github.com/steakhal approved this pull request.

Thanks. I think it looks great!
I had one remark that I unresolved where we had some misunderstanding, but even that it's probably not a big deal.

https://github.com/llvm/llvm-project/pull/191333