[llvm] [Symbolizer, DebugInfo] Clean up LLVMSymbolizer API: const string& -> StringRef (PR #104541)

[James Henderson via llvm-commits]

https://github.com/jh7370 commented:

I had this vague idea in my mind that there was a good reason we weren't using `StringRef` here. However, I now can't think of a good reason why that could still be the case, given that `StringRef` is already in use in the same code.

@dwblaikie, any thoughts?

https://github.com/llvm/llvm-project/pull/104541