RoundRobinGroupTargetWriteAsyncThreadSafe Method

Ensures forwarding happens without holding lock

Writes an array of logging events to the log target, in a thread safe manner. Any override of this method has to provide their own synchronization mechanism. !WARNING! Custom targets should only override this method if able to provide their own synchronization mechanism. Layout-objects are not guaranteed to be thread-safe, so using them without a SyncRoot-object can be dangerous.