Summary:
For history of the experimental version see folly/experimental/hazptr

Added:
- Support for deterministic schedule testing.

Fixes:
- Eliminates performance pathological cases for hazptr_array and hazptr_local construction when a thread cache can only partially satisfy the needed number of hazptr_holder-s.
- try_protect sets ptr to the value read from src on success. Otherwise, ptr may be used by the client code when it is invalid.

Code improvements including:
- Using separate files for different components.
- Eliminated all macro definitions except one.
- Simplified thread local structures.

Reviewed By: davidtgoldblatt

Differential Revision: D7565357

fbshipit-source-id: fb00fad7395148e66d6231a374b5b717574ed270