[clang] [Clang] allow `` `@$ `` in raw string delimiters in C++26 (PR #93216)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

LGTM but I would like Tom or Aaron to also take a look

https://github.com/llvm/llvm-project/pull/93216