Add `nonzero_static()` op to pytorch to unblock export (#97417)
Summary: Add new experimental python op (`torch.nonzero_static`) for export. There is NO cuda impl included in this PR
Example:
Say input tensor is `x = torch.tensor([[1, 0], [3, 2]])`
call regular `nonzero()` on x will give you a tensor `tensor([[0, 0], [1, 0], [1, 1])`
call `nonzero_static(x, size=4)` on x will give you a tensor `tensor([[0, 0], [1, 0], [1, 1], [fill_value, fill_value])` (padded)
call `nonzero_static(x, size=2)` on x will give you a tensor `tensor([[0, 0], [1, 0])` (truncated)
Test Plan:
**Unit Tests**
```
buck test @mode/dev-nosan //caffe2/test:test_dynamo -- 'caffe2/test:test_dynamo - test_export.py::ExportTests::test_export_with_nonzero_static' -- 'caffe2/test:test_dynamo - test_misc.py::MiscTests::test_nonzero_static'
```
**PT2 Export with `nonzero_static()`**
Example of `GraphModule` in the exported graph
```
def forward(self, x):
arg0, = fx_pytree.tree_flatten_spec(([x], {}), self._in_spec)
nonzero_static_default = torch.ops.aten.nonzero_static.default(arg0, size = 4); arg0 = None
return pytree.tree_unflatten([nonzero_static_default], self._out_spec)
```
Differential Revision: D44324808
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97417
Approved by: https://github.com/ezyang
