Allow ByteStreamRDP_OutputSvc to handle multiple events on the fly
Make an EventContext-aware ByteStreamRDP_OutputSvc::putEvent method and ensure all events on the fly are kept in memory. Previously, adding an event to the next slot was deleting the data from the previous slot leading to segfaults. Fixes ATR-21497.
The context-aware version of the method is also added in the interface with a dummy implementation in other derived classes. The other clients rely on retrieving EventInfo from event store in putEvent, so in the future it may be worth moving this retrieve to a context-aware ReadHandle. That's why the context-aware putEvent is worth adding in the interface and not just in ByteStreamRDP_OutputSvc.
Also added missing override keywords in the ByteStreamOutputSvc derived classes.