Refactor and improve make_fx testing (#103196)
This is in preparation for the custom_op_compile_check utility, which
will call the newly refactored function.
This PR:
- splits off code into helper functions
- adds clearer error messages
- stops updating the inputs destructively (leading to slightly slower
tests)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103196
Approved by: https://github.com/bdhirsh, https://github.com/soulitzer
