[Nested Tensor] Create differentiable nt to tensor view functions (#83371)
This PR attempts to implements 2) "the safe way" of creating a view of nested tensor that returns a regular tensor. The rest of the break down is here: https://fb.quip.com/J8QCAx41af11
https://gist.github.com/drisspg/8622e9c97d374fa920ac647e1167cabc
This is a short list of some edge cases. After some more work I was able to address two of the test cases in the above gist. There are few complex aspects here that I left defeated comments inline.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83371
Approved by: https://github.com/bdhirsh
