Investigate and possibly convert to StampedLock for OffHeap

We currently use an array of ReentrantReadWriteLock entries to protect critical sections of a off heap map. We shouldn't require reentrancy for our various operations and thus we should be able to hopefully drop in replace these with the equivalent StampedLock write lock instances.

Doug Lea mentions this is the fastest lock they have https://concurrency.markmail.org/thread/kfdv6tg3tnutl4ts