Add new tls snapshot feature (#72832)
Summary:
Reland of https://github.com/pytorch/pytorch/pull/72623 that was reverted for the tls cleanup was removed.
From close inspection on the counting of the number of available keys, I think there is one more since the guard is actually one after the last usable key. With this update assert, the last updated key will still be <=63 which will fit just fine.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72832
Reviewed By: H-Huang
Differential Revision: D34228571
Pulled By: albanD
fbshipit-source-id: ce5e10a841ea87386727346cfc8d9327252574c4
(cherry picked from commit 59d3b863534a37ac3463e2814bc9599c322669ee)
