[llvm] [mlir][bazel] Build MLIR bindings extensions with `nanobind_bazel` (PR #169306)

[Keith Smiley via llvm-commits]

keith wrote:

nice, i started working on this one too. i went a different path and was updating the upstream `nanobind` target, which would be a drop in replacement for what we have today. to me the interesting question is what we expect from downstream users for this. because right now i guess folks have likely roughly copy pasted what is here

https://github.com/llvm/llvm-project/pull/169306