[PT2E][Quant][BE] Split short term and long term tests in different files (#99065)
Just for better organization
Differential Revision: [D44918492](https://our.internmc.facebook.com/intern/diff/D44918492/)
**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D44918492/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99065
Approved by: https://github.com/jerryzh168
