Expose RttVariance statistic

[jarnovanderlinden]

Describe the feature you'd like supported

Expose the RttVariance of a connection in the connection statistics API.

Proposed solution

In order to inform the amount of buffering needed for media streaming, I'd like to know the variance in the Rtt of a connection. MsQuic already tracks this internally as RttVariance. It would be nice if this was available through the connection statistics alongside the currently available (smoothed) Rtt, MinRtt, and MaxRtt.

Using the MinRtt and MaxRtt isn't quite what I need as they are over the lifetime of the connection. The max in particular can be subject to transients during startup of the connection, and may therefore not reflect the behaviour of the connection during normal operations.

Additional context

No response

[nibanks]

Feel free to create a PR exposing this, but please keep in mind it must not be a breaking change (i.e. new stats go at the end of the struct). Thanks!