[caffe2] Fix pybind11 native python link error (#92325)
Summary:
Currently, we define some C++ functions in one C++ Python extension
which are used by another. This happens to work, but isn't guaranteed to.
This diff moves these functions to a separate C++ library rule to fix this.
Test Plan: CI
Differential Revision: D42552515
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92325
Approved by: https://github.com/kit1980, https://github.com/Skylion007
