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

[Oliver Hunt via cfe-commits]

ojhunt wrote:

Also the associated tests do not pass yet as they're blocked on https://github.com/llvm/llvm-project/pull/136828 and other ptrauth PRs

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