Improve quic:stream_state_updated

[rmarx]

As reported by @hlandau on the mailing list:

quic:stream_state_updated:

I think this needs to be clarified a little that an event logged here with both
a stream_id field and a stream_side field is expressing a state for that
component of the stream and from the perspective of the specified vantage point
(also, what about the network vantage point?); whereas an event logged here
with a stream_id field but no stream_side field is expressing a state for
both stream components as a whole.

If my interpretation here is correct, I think it would also help to note that
the valid values of StreamState depend on the value and presence of
stream_side.

[rmarx]

Specifically for the "network vantage point" aspect of the question: the intent was that a network observer would use "sending" vs "receiving" depending on which party opened the stream, but that indeed falls down when using bidi streams...

I think there is some overlap here with the stream_state values and their implied-ness for either one or both sides, but I think @LPardue has a better grasp on this than me.

[rmarx]

@LPardue could use some input on this here :)

[LPardue]

I have never used this event myself and have little experience to impart. There's no text to describe how stream_side is supposed to be used, which isn't great.

Not sure what to do here tbh