Enable autograd wrt sparse CSR tensors
This pull request enables accumulating gradients for the CSR tensor.
Functions that work and are tested:
- tensor.abs()
- tensor.neg()
- tensor.conj_physical()
- torch.addmm
`torch.mm` also works, but tests will be added later.
In addition, this PR adds throwing an error when trying to access strides, storage, and contiguity info on a CSR tensor.
`tensor.to_sparse_csr().to_sparse_csr()` was failing and now fixed.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75435
Approved by: https://github.com/cpuhrsch
