Move thnvrtc and DynamicLibrary to ATen (#22362)
Summary:
Having the NVRTC stub in ATen is necessary to call driver APIs in ATen. This is currently blocking https://github.com/pytorch/pytorch/pull/22229.
`DynamicLibrary` is also moved as it is used in the stub code, and seems general enough.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22362
Differential Revision: D16131787
Pulled By: ezyang
fbshipit-source-id: add2ee8a8865229578aa00001a00d5a6671e0e73
