[Operator Versioning] Split the upgrader test to a separate file and …

…cover mobile part (pytorch#70090)

Summary:
1. Split the test `test_save_load.py` to two files. Basically move the operator versioning related changes to `test_save_load_for_op_versions.py`.
2. Add mobile module related test to `test_save_load_for_op_versions.py`

How to run:
```
buck test mode/opt //caffe2/test:jit
or
python test/test_jit.py TestSaveLoadForOpVersion
```

Pull Request resolved: pytorch#70090

ghstack-source-id: 146103547

Test Plan:
```
buck test mode/opt //caffe2/test:jit
python test/test_jit.py TestSaveLoadForOpVersion
```

Reviewed By: tugsbayasgalan

Differential Revision: D33180767

fbshipit-source-id: dd31e313c81e90b598ea9dd5ad04a853c017f994