Normalize DLPack stride to 1 where shape < 2 (#83158)
Fixes #83069. Also move all the dlpack tests to a new file., `test_dlpack.py`.
The fix involves always allocating a "strides" int array when converting to dlPack and deleting the strides when the capsule descructor is called. Then the strides are copied from the tensor, and `strides[i]` is set to `1` where `shape[i] < 2`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83158
Approved by: https://github.com/ezyang
