[llvm] [mlir] [mlir][Python] create MLIRPythonSupport (PR #171775)

[Alex Trotta via llvm-commits]

Ahajha wrote:

@makslevental Sure, I can take a look tomorrow. Main things I'll look for/can forsee being issues:
- Bazel build (need to see if there are any other changes necessary).
- More shared libraries, wrt/Bazel. We have two extensions and just statically link nanobind into both, we will probably want to continue doing that. Not sure if we want to expose that configurability, but I also need to understand the context more.
- General test to make sure it keeps working in our repo.

https://github.com/llvm/llvm-project/pull/171775