Deliver messages even when events are skipped

[mmcshane]

What was changed

Here we switch to delivering all messages dependent on events IDs less than or equal to the current event ID.

Why?

We don't run WFTScheduledEvent instances through standard event handling so we were missing messages dependent on events of that type

Checklist

1. Closes

2. How was this tested:

Unit & features

3. Any docs updates needed?

[cretz]

Would it have value to ask the server to always deliver these in event ID order?

Also, is the number of these so great that you really need to sort because of fear of the cost of takeLTE? I think you can just make takeLTE iterate over all messages every time and https://github.com/golang/go/wiki/SliceTricks#filter-in-place to keep the ones greater than while extracting the ones less than or equal.

So something like this (untested, just typed here in comments):

func (emi *eventMsgIndex) takeLTE(eventID int64) (out []*protocolpb.Message) {
	n := 0
	for _, msg := range *emi {
		if msg.GetEventID() > eventID {
			(*emi)[n] = msg
			n++
		} else {
			out = append(out, msg)
		}
	}
	*emi = *emi[:n]
	return;
}

[mmcshane]

I'm fine with doing a little more work in takeLTE. I would expect the number of messages per WFT to be low (which to be fair, also makes sorting cheap) but there may be a substantial number when we rebundle into a bigger WFT for replay. I'd like to preserve the transport's ability to reorder messages until we learn more about what is desirable at that layer.