[SR] Generalize VarStackNodeWrapper (#71573)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71573
Many ops (`gather_ranges_to_dense`, `sigrid_transforms`, etc) are implemented like this:
```
void op_out_(std::vector<Tensor>& output) {
// actual op implementation
}
std::vector<Tensor> op() {
std::vector<Tensor> outputs;
// populate outputs with empty tensors
op_out_(outputs)
return outputs;
}
```
This pattern is not ideal for ops that are fused with `ListUnpack` - it would be better if we wrote to the outputs directly.
This diff extends the ideas from `VarStackNodeWrapper` to allow for this. The changes are:
* `s/VarStackNodeWrapper/ProcessedNodeInputWrapper`. The old name was bad because the class is more general than the `VarStack` use case. Also moved the class to `processed_node_wrapper.h`
* Add a `ProcessedNodeOutputWrapper`; it's essentially the same idea as `ProcessedNodeInputWrapper`, but it allows non-const access to the underlying tensors.
* These classes are very similar, so CRTP is used to facilitate code re-use
ghstack-source-id: 148825800
Test Plan: `buck test caffe2/benchmarks/static_runtime:static_runtime_cpptest -- Stack`
Reviewed By: swolchok
Differential Revision: D33687965
fbshipit-source-id: 5fa0107211116867bb2b63968c126550d32fbea6
(cherry picked from commit 75c263d960a876e4db84c129e6cff2a770a3cd29)
