The purpose is to be able to create a RtpPacketSendInfo from Pacing and RtpPacketSendInfo only.
This allow further refactoring where we directly in PacketRouter can notify BWE and early loss detection that a packet will be sent.
RtpPacketSendInfo::From is mostly added to be able to test conversion.
Bug: webrtc:15368
Change-Id: I5ebe2dc91d2eedf2c86e62c3f9738437082a49e4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/343766
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41961}
