[clang] [clang/AST] Make it possible to use SwiftAttr in type context (PR #108631)

[Pavel Yaskevich via cfe-commits]

xedin wrote:

I addressed most of the comments. A few points to add:

- I'm not sure what to make of the comment regarding templates if somebody could point me to the right direction I can make appropriate changes
- I'd need some guidance regarding release note
- I'd prefer to keep AttributedType changes in this PR since they are integral part of the swift_attr change.

https://github.com/llvm/llvm-project/pull/108631