[clang] [Clang][TableGen] Use StringRef in FlattenedSpelling (PR #113809)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM; I think this is relying on reasonably safe assumptions -- at least, I couldn't find any places where we were pushing data into the flattened spelling and it wasn't longer-lived than the `FlattenedSpelling` object itself.

https://github.com/llvm/llvm-project/pull/113809