[clang] [clang][AST] Hash `AttributedType`'s `Attr` by Content (PR #200961)

[Qiongsi Wu via cfe-commits]

qiongsiwu wrote:

@hnrklssn Thanks again for the review. I've completely revamped this PR to handle the argument content in a more general way. I am basically drawing a parallel with the equivalence check, and I am using tablegen to automatically take the arguments into account. 

https://github.com/llvm/llvm-project/pull/200961