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

torchgen/native_function_generation.py

@@ -336,6 +336,7 @@ def generate_function(
             cpp_no_default_args=set(),
             is_abstract=f.is_abstract,
             has_composite_implicit_autograd_kernel=False,
+            has_composite_implicit_autograd_nested_tensor_kernel=False,
             has_composite_explicit_autograd_kernel=True,
             has_composite_explicit_autograd_non_functional_kernel=False,
             # Every generated NativeFunction gets a "generated" tag, so it's easy to tell