SCReAM: Scale backoff by feedback interval and reset ref window on congestion

This CL:
1. Tracks feedback interval in ScreamV2 and scales backoff relative
   to effective virtual RTT (max of virtual RTT and feedback interval)
   to account for how often feedback actually arrives. This avoids
   stalled backoff during low bitrate audio with large feedback intervals.
2. Clamps the reference window to data in flight on first congestion
   in delay-based congestion control to eliminate initial rampup overshoot.
3. Adds 'FeedbackIntervalAvgG' and 'UseFeedbackIntervalForVirtualRtt'
   parameters to ScreamV2Parameters.
4. Tightens expectations in AudioOnlyBothDirectionsLinkCapacity40To90KbpsRtt200ms
   to reflect lower RTT and tighter BWE.

Bug: webrtc:447037083
Change-Id: I79d8cfff9e4ac034d8192a3668ea3342812ce141
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/506900
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48777}