Re-add benchmarking files to ios TestApp (#85539)
Fixes #76033
The benchmarking code in the iOS TestApp was removed a while back as dead code:
https://github.com/pytorch/pytorch/pull/64849
I believe this was done in error - as this leaves our TestApp empty, nothing occurs when it runs. And we still have a tutorial up demonstrating how to use the benchmarking feature of the TestApp.
This diff restores the files that were deleted, with some minor tweaks for compatibility with changes that have happened since they were deleted.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85539
Approved by: https://github.com/kimishpatel
