[llvm] [mlir] [Dwarf] Support `__ptrauth` qualifier in metadata nodes (PR #83862)

[Fangrui Song via llvm-commits]

MaskRay wrote:

I was confused as I haven't attended any [LLVM Pointer Authentication sync-ups](https://discourse.llvm.org/t/llvm-pointer-authentication-sync-ups/62661) and I am definitely lacking context. It seems that there is an upstreaming proposal back in 2019 https://discourse.llvm.org/t/rfc-pointer-authentication-for-arm64e/53433 and apple/llvm-project contains these `DW_TAG_LLVM_ptrauth_type` changes. This PR is part of the upstream efforts. Yeah, looks good to me.

Normally, when I see `createPtrAuthQualifiedType` with no in-tree user, I'd ask that you prepare links for the immediate user.

https://github.com/llvm/llvm-project/pull/83862