cherry-pick: Reorganize + Upgrade Dynamo (release/1.4)

[gs-olive]

Description

• Cherry-pick of fix: Reorganize Dynamo directory + backends #1928 for release/1.4
• Cherry-pick of fix: Improve partitioning + lowering systems in torch.compile path #1879 for release/1.4

Type of change

• Cherry-pick to release branch

Checklist:

• [ x ] My code follows the style guidelines of this project (You can use the linters)
• [ x ] I have performed a self-review of my own code
• [ x ] I have commented my code, particularly in hard-to-understand areas and hacks
• [ x ] I have made corresponding changes to the documentation
• [ x ] I have added tests to verify my fix or my feature
• [ x ] New and existing unit tests pass locally with my changes
• [ x ] I have added the relevant labels to my PR in so that relevant reviewers are notified

[github-actions]

Code conforms to C++ style guidelines

[github-actions]

Code conforms to Python style guidelines

[github-actions]

Code conforms to C++ style guidelines

[github-actions]

Code conforms to Python style guidelines