Video timing simulator: Add RTX support.

This change adds RTX reception support to the video timing simulator.
This is done by introducing `Receiver`, which demuxes the stream of RTP
packets (video + RTX), so that video packets are passed through but RTX
packets are decapsulated. The resulting recovered stream is then sent to
the existing `Assembler` and then the pipeline continues as usual from
there.

Other related and required changes:
- Update `RtpPacketSimulator` to handle logged packets with RTX OSN.
- Update the stream factories to feed simulated packets to the `Receiver`, instead of the `Assembler`.
- Enable NACKing in `Assembler` by creating a `NackRequester` and corresponding `NackPeriodicProcessor`. (Without this, the jitter buffer adaptation for frames with recovered packets will be incorrectly done.)
- Add simulation-level smoke tests for a lossy RtcEventLog scenario.

Bug: b/423646186
Change-Id: I2bdccca07107234c148300629dd45e831ee61158
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/432961
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46755}