Move autograd metadata from VariableImpl to TensorImpl (#13827)
Summary:
Changes originally in this PR:
1. Move Variable::Impl data members into TensorImpl as `AutogradMeta` struct
2. Change Variable::Impl functions to use data members in `AutogradMeta` struct
3. Add `shallow_copy_and_detach()` function to each subclass of TensorImpl
4. Do shallow copy when the user calls `make_variable(tensor)` / `make_variable_view(tensor)` / `variable.set_data(tensor)` / `variable.detach()`
Changes moved from https://github.com/pytorch/pytorch/pull/13645:
1. Add a flag to Variable to disallow size/stride/storage_ptr changes from in-place operations such as `resize_` / `resize_as_` / `set_` / `transpose_`, and set this flag to true when people call `tensor.data` in Python.
2. Write text in the docs to actively discourage changing the shape or storage of `tensor_detached` and expecting `tensor` to also be updated.
This is the 1st+2nd PR mentioned in https://github.com/pytorch/pytorch/issues/13638.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/13827
Differential Revision: D13507173
Pulled By: yf225
fbshipit-source-id: b177b08438d534a8197e34e1ad4a837e2db0ed6a
