Implement shallow copy functions for `FunctionalTensorWrapper`. (#118783)
Fix: #115792
This PR implements 2 virtual functions of `TensorImpl` that are called when setting the
`tensor.data`:
- `shallow_copy_from`: which calls `copy_tensor_metadata`; and
- `copy_tensor_metadata`: which copies all `FunctionalTensorWrapper` metadata and ~calls
`dest->value_.set_data(src->value_)`~ assigns `dest->value_ = src->value_`, so as to copy also the inner tensor using the same
method
Before this PR, the inner tensor of a `FunctionalTensorWrapper` was being ignored.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/118783
Approved by: https://github.com/bdhirsh
