Setup torch/csrc/functorch/*; move CompileCache.{h, cpp} there (#85263)
The plan for functorch C++ is:
- all C++-only code goes into aten/functorch.
- any C++ code with a python dependency goes into torch/csrc/functorch. This will include the functorch Python bindings as well as all of torchdim.
Alternative:
- we could split it so that code goes into torch/csrc/functorch/nopython and torch/csrc/functorch/python instead of putting anything into ATen. This just feels like a matter of cosmetics.
This PR also does two more things:
- fix a windows lint error regarding PyLong_asLong
- clang-format the code (because the linter got triggered)
Test Plan:
- run tests
- check internal build
Fixes #ISSUE_NUMBER
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85263
Approved by: https://github.com/ezyang
