Support tensor iterator

[kparichay]

Tensor does not support an iterator. It is basic to iterate over a tensor if its memory of contiguous, but with strided access, a proper lightweight operator is needed.

[taos-ci]

:octocat: cibot: Thank you for posting issue #1668. The person in charge will reply soon.

[zhoonit]

reference: https://numpy.org/doc/stable/reference/arrays.nditer.html

Somewhat(?) related issue #704

[kparichay]

Yeah, that's a good related interface. A similar interface is needed but has to be lightweight. I was thinking more closer c++ iterators where next() in the iterator should handle the stride internally.