[Profiler][Minor] Separate standalone profilers from the main PyTorch profiler. (#85511)
There are a number of instrumentation utils which have been added to the profiler toolkit. They are generally small and self contained, often wrapping vendor APIs. (NVTX, ITT)
They don't really interact with the much more expansive machinery of the PyTorch profiler beyond registration / unregistration, minor util sharing, and reusing the profiler base class. Just as in the case of stubs, it makes sense to group them in a dedicated subfolder.
Differential Revision: [D39108649](https://our.internmc.facebook.com/intern/diff/D39108649/)
**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D39108649/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85511
Approved by: https://github.com/albanD
