[clang] [clang] Prevent dangling StringRefs (PR #98699)

[Shafik Yaghmour via cfe-commits]

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

It looks like we are using the same pattern that fix is using in `ASTStmtReader::VisitRequiresExpr` which gives me some comfort but I am not happy that we have a relatively complex and easy to get wrong operation repeated in three places now. This feel like it should be refactored into common code and if we find a bug w/ it later on fixing it one place will fix all the places.

https://github.com/llvm/llvm-project/pull/98699