[llvm] Reland "[bazel][mlir][python] Port #155741: stub auto-generation" (PR #159940)

[Jordan Rupprecht via llvm-commits]

rupprecht wrote:

> All that's left is the `WORKSPACE`, indifferent if this gets merged now (we don't use it), but someone else might want it.

Same, I had bumped the version to 2.9.2 because I thought we might need it, but we don't. I think we might as well use the same version for consistency though.

https://github.com/llvm/llvm-project/pull/159940