[llvm] [IR2Vec] Add triplet generation utility script for vocabulary training (PR #149215)

[S. VenkataKeerthy via llvm-commits]

svkeerthy wrote:

### Merge activity

* **Jul 30, 5:06 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/149215).


https://github.com/llvm/llvm-project/pull/149215