[llvm] [SandboxIR] Boilerplate code (PR #95814)

[Arthur Eubanks via llvm-commits]

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

putting this in top level under `llvm/` as opposed to under `llvm/Transforms` makes more sense, lgtm

https://github.com/llvm/llvm-project/pull/95814