vTensor cleanup 1/N - swap order of vTensor and vTensorStorage in cpp file (#5421)

Summary:
Pull Request resolved: #5421

## Context

TSIA; swap the order of `vTensorStorage` and `vTensor` function implementations in the `Tensor.cpp` file, such that it matches the order of declaration in the `Tensor.h` header file. I don't recall why the ordering was not consistent before.
ghstack-source-id: 243061029
exported-using-ghexport

Reviewed By: jorgep31415

Differential Revision: D62878648

fbshipit-source-id: 4ac4d54bc8bc0d8aa30422e599e9605a7b351e33

Author: SS-JIA