[llvm] [IR2Vec] Add llvm-ir2vec tool for generating triplet embeddings (PR #147842)

[S. VenkataKeerthy via llvm-commits]

svkeerthy wrote:

### Merge activity

* **Jul 17, 6:58 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/147842).


https://github.com/llvm/llvm-project/pull/147842