pytorch

b0722451 - [dtensor][4/N] refactor dispatching logic and add propagator (#90733)

[dtensor][4/N] refactor dispatching logic and add propagator (#90733) This PR refactors the dispatching logic to make it more clean, and isolate the sharding propagation logic out to a separate class. This is so that we can implement more complicated propagation features later. Differential Revision: [D42876251](https://our.internmc.facebook.com/intern/diff/D42876251) Pull Request resolved: https://github.com/pytorch/pytorch/pull/90733 Approved by: https://github.com/XilunWu, https://github.com/fduwjj