Unboxed kernels in c10 (#23447)
Summary:
The c10 dispatcher now also stores a `void*` pointer to the unboxed kernel function and this kernel function can be called if the call site knows the exact kernel signature.
It is not clear if this API will survive in the long term, but in the short term this allows an easier migration from ATen to c10 and is supposed to replace ATenDispatch.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23447
ghstack-source-id: 88050435
Differential Revision: D16521939
fbshipit-source-id: 7e570df5a721defc677c3cc91758651dbe06ce1c
