backport std::ssize to c10
Summary:
Now that we have -Werror=sign-compare enabled, we encounter a lot of
friction comparing standard containers and our tensors which are
signed.
std::ssize will make it easier and safer to succinctly convert
container sizes to a signed type.
Test Plan: Added a unit test.
Reviewers: ezyang
Subscribers:
Tasks:
Tags:
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* #97443
* __->__ #97442
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97442
Approved by: https://github.com/ezyang
