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

[Pavel Yaskevich via cfe-commits]

xedin wrote:

@erichkeane I don't think swift_attr is intended in that context but I don't see how these changes regress existing uses.

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