[clang] [clang][ptrauth] Add support for querying the ptrauth schema of a type (PR #138482)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> This should come with a release note so users know about the new builtins, right?

I'm wondering if we should actually just have the release notes say something like "Added support for ARMv{revision} pointer authentication, see the `pointer authentication` section for details, and then just have all the pointer authentication stuff (qualifiers, builtins, etc) there? Otherwise I think we end up flooding the releases notes with "added ptrauth qualifier" "added this ptrauth builtin" "added this other pointer auth builtin" "added this ptrauth feature", etc

We also obviously have to upstream the full pointer auth docs as well, but I think it makes sense to delay that until we're more confident we have all the important parts upstreamed/

https://github.com/llvm/llvm-project/pull/138482