[llvm] [memprof] Add CallStackRadixTreeBuilder (PR #93784)

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson commented:

Started a review, but am confused about what "Indexes" is - can you clarify that with a more intuitive description? I added a few other comments too but will finish the review once I have a better understanding of that vector.

https://github.com/llvm/llvm-project/pull/93784