Stores thread-local lock info and manages the association of this info with each ReaderWriterLock owned by a thread. The original code maintained lists of thread-local lock entries on the CLR's thread objects, and manually released lock entries, which involved walking through all threads. While this is possible with ThreadLocal, this implementation prefers to use a similar design to that from ReaderWriterLockSlim, and allow reusing free entries without removing entries, since it is unlikely that the list length for any thread would get unreasonably long.
