Pace CCFB using actual wire overhead and is_bandwidth_limited status

This CL improves the RFC 8888 Congestion Control Feedback (CCFB) pacing logic to accurately calculate pacing delays and respect bandwidth limits:

1. **Wire Overhead Inclusion**: Includes the IP/UDP/SRTP wire overhead (defaulting to 42 bytes) in the CCFB pacing debt calculation. This prevents the generator from underestimating the feedback transmission rate and exceeding configured bandwidth limits on high packet rate connections.
2. **Bandwidth-Limited Pacing**: Only applies the feedback fraction limit (e.g., 5% of send BWE, if configured via the `feedback_fraction` option in the `WebRTC-RFC8888CongestionControlFeedback` field trial) when the link is actually marked as bandwidth-limited (`is_bandwidth_limited = true`). When not bandwidth-limited, the default pacing rate (500 kbps) applies.
3. **API Deprecation**: Deprecates the old `OnSendBandwidthEstimateChanged(DataRate)` signature in favor of a new one carrying `is_bandwidth_limited` and `transport_overhead` parameters.

These changes ensure CCFB complies with the RFC 8888 recommendation to not consume excessive feedback bandwidth (restricting it to a safe fraction of BWE when congested), while keeping feedback responsive and pacing correctly.

Bug: webrtc:519655843
Change-Id: I7b1b40f1f711df76b7beb4718b1566dd9d48aef5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/478442
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47951}