[FX acc]Store shape and dtype in serialized output node args (#52462)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/52462
This is the step one for supporting multiple outputs in fx nnpi path.
During serialization, we store the shape and dtype in output args, so that importer doesn't need to go back and find the nodes.
The output nodes will looks like
```
{
"target": "output",
"op_code": "output",
"name": "output",
"args": [
{
"is_node": true,
"name": "add_1",
"shape": "[1, 1]",
"dtype": "torch.float32"
}
],
"kwargs": {}
}
```
Test Plan: Doesn't break existing tests and will test on step two.
Reviewed By: jfix71
Differential Revision: D26500742
fbshipit-source-id: 755d2dec704d9da579af40e754b556d6c01aa796
