Make various improvements to C++ API parity test harness (#25828)
Summary:
This PR makes the following improvements to C++ API parity test harness:
1. Remove `options_args` since we can get the list of options from the Python module constructor args.
2. Add test for mapping `int` or `tuple` in Python module constructor args to `ExpandingArray` in C++ module options.
3. Use regex to split up e.g. `(1, {2, 3}, 4)` into `['1', '{2, 3}', '4']` for `cpp_default_constructor_args`.
4. Add options arg accessor tests in `_test_torch_nn_module_ctor_args`.
We will be able to merge https://github.com/pytorch/pytorch/pull/24160 and https://github.com/pytorch/pytorch/pull/24860 after these improvements.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25828
Differential Revision: D17266197
Pulled By: yf225
fbshipit-source-id: 96d0d4a2fcc4b47cd1782d4df2c9bac107dec3f9
