Re-land sym_numel (#82374) (#82726) (#82731)
This PR relands sym_numel #82374 and fixes the ios build break in this commit : https://github.com/pytorch/pytorch/pull/82731/commits/8cbd0031c551b290bab0d0bae0ef6c46e1192853
which was a type mismatch in an equality.
### Description
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### Issue
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### Testing
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Pull Request resolved: https://github.com/pytorch/pytorch/pull/82731
Approved by: https://github.com/malfet
