Configure RTX at construction of the RTP module

The RTX mode and payload types were being set right after the RTP module
had been created. That kept RTPSender's RTX state mutable, which
requires a lock for every read of the RTX mode.

* Add rtx mode and payload types to RtpRtcpInterface::Configuration
* Apply them when constructing RTPSender.
* RtpVideoSender now passes the RTX configuration at creation.
* Remove SetRtxSendStatus() and SetRtxSendPayloadType() from
  RtpRtcpInterface and ModuleRtpRtcpImpl2.
* Deprecate RTPSender::SetRtxStatus() and SetRtxPayloadType(). Once
  direct users of RTPSender have migrated, they can be removed and the
  RTX state made const.

Invalid configurations still log an error and leave RTX off. Since all
RTX payload types are now applied at once, a single invalid one drops
the whole mapping. This keeps RTX off for a simulcast layer whose codec
has no RTX payload type, as before. Keeping just the RED mapping would
enable RTX without a way to retransmit media packets.

Bug: webrtc:42223727
Change-Id: I34be4f765293599fc2358c4ab52cebe1fcdb98d0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/507340
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48836}