fx quant: add a BC test for loading old torch.package models (#65538)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65538
Adds a test which verifies that `prepare_fx` and `convert_fx` work
on models created by `torch.package` in the past. In detail:
1. (one time) create a model and save it with torch.package. Also save input,
expected output, and names of quantization related get_attrs added by
our passes.
2. (every time) load the model from (1), and verify that expected output
matches current output, and that get_attr targets did not change.
Test Plan:
```
python test/test_quantization.py TestSerialization.test_linear_relu_package_quantization_transforms
```
Imported from OSS
Reviewed By: supriyar
Differential Revision: D31512939
fbshipit-source-id: 718ad5fb66e09b6b31796ebe0dc698186e9a659f
