Better reshape with autograd support (#82754) (#84154)
The original author is @YifanShenSZ and the original PR is: #82754
# Summary:
Previous reshape [https://github.com/pytorch/pytorch/issues/80981](https://github.com/pytorch/pytorch/pull/80981) is ok for forward, but needs improvement for backward: need to handle "sometimes view sometimes copy" behavior.
This pull request fixes it by:
1. add a new alias dispatch key `CompositeImplicitAutogradNestedTensor`, which ideally would work as nested-tensor version of `CompositeImplicitAutograd`
2. register `reshape_nested` to `reshape` by `CompositeImplicitAutogradNestedTensor`
Side changes:
* add contiguous memory format support to `clone_nested`
* add `view_nested`
* add `reshape_as_nested`
Fix issue [https://github.com/pytorch/pytorch/issues/83041](https://github.com/pytorch/pytorch/issues/83041)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82754
Test Plan:
Imported from GitHub, without a `Test Plan:` line.
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Reviewed By: albanD
Differential Revision: D39023822
Pulled By: drisspg
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84154
Approved by: https://github.com/bdhirsh, https://github.com/albanD
