[Profiler] Move Allocation into EventType.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77694
Continuing the trend of unification, this PR removes the special path for allocation tracking. The overall delta is pretty minimal; it's mostly just extending and unifying visitors. This also comes with the added benefit that memory profiling now gets to take advantage of the lock-free machinery.
Differential Revision: [D36189043](https://our.internmc.facebook.com/intern/diff/D36189043/)
Approved by: https://github.com/aaronenyeshi
