FEditorAnalyticsSession::LogEvent

Append an event to the session log. The function is meant to record concurrent events, especially during a crash with minimum contention. The logger appends and persists the events of interest locklessly on spot as opposed to overriding existing values in the key-store. Appending is better because it prevent dealing with event ordering on the spot (no synchronization needed) and will preserve more information.

@note They key-store is not easily usable in a 'lockless' fashion. On Windows, the OS provides thread safe API to modify the registry (add/update). On Mac/Linux, the key-store is a simple file and without synchronization, concurrent writes will likely corrupt the file.