Add a mutex for the ap_handle_list

Add a mutex for the ap_handle_list

In CLR environment, GC can release an ap handle in non-main thread.
The problem is that add() operation for an ap handle can arise during GC
working in main or other thread. In this case, the ap_handle_list is accessed
at the same time in main and non-main thread.
This can make a memory corruption of the ap_handle_list.

Change-Id: I7e6a37751e746153d2f6610fc340b44c1e498f25