[clang] [CIR] Add metadata type, attributes and metadata_as_value op. (PR #204190)

[Andy Kaylor via cfe-commits]

https://github.com/andykaylor requested changes to this pull request.

Can you tell me more about how you intend to use this? This is a very low-level representation. I'd prefer to have less direct coupling with the LLVM IR form in CIR.

https://github.com/llvm/llvm-project/pull/204190