[DataLoader2] Fix apply_sharding to accept one sharding_filter per branch (#90769)
Changes:
- Allow multiple `sharding_filter` in the pipeline as long as they are not on the same branch
- [x] Add test
Example:
```mermaid
graph TD;
DP1-->sharding_filter_1;
sharding_filter_1-->DP3;
DP2-->sharding_filter_2;
sharding_filter_2-->DP4;
DP3-->DP4;
DP4-->output;
```
In order to properly shard `DP1` and `DP2`, we should allow multiple `sharding_filter`s
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90769
Approved by: https://github.com/NivekT
pytorch
7a112c43 - [DataLoader2] Fix apply_sharding to accept one sharding_filter per branch (#90769)
