Pass initial video CSRCs via RtpConfig

WebRtcVideoSendStream called SetCsrcs() right after creating the
VideoSendStream to apply the CSRCs from the RTP parameters. Add a csrcs
field to RtpConfig, like AudioSendStream::Config::Rtp::csrcs, and pass
them at creation instead, so that RtpVideoSender is initialized with
them. SetCsrcs() is still used for updates from setParameters().

Bug: webrtc:42223727
Change-Id: Id34d8c8d46b6ad63fa0150c7892b029f5fc6a30d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/506220
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48778}