Refactoring PayloadRouter.

- Move PayloadRouter to RtpTransportControllerInterface.
- Move RetransmissionLimiter inside RtpTransportControllerSend from
  VideoSendStreamImpl.
- Move video RTP specifics into PayloadRouter, in particular ownership
  of the RTP modules.
- PayloadRouter now contains all video specific RTP code, and will be
  renamed in a follow-up to VideoRtpSender.
- Introduce VideoRtpSenderInterface.

Bug: webrtc:9517
Change-Id: I1c7b293fa6f9c320286c80533b3c584498034a38
Reviewed-on: https://webrtc-review.googlesource.com/88240
Commit-Queue: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24009}

video/video_stream_encoder.h

@@ -21,7 +21,6 @@
 #include "api/video/video_sink_interface.h"
 #include "api/video/video_stream_encoder_interface.h"
 #include "api/video_codecs/video_encoder.h"
-#include "call/call.h"
 #include "call/video_send_stream.h"
 #include "common_types.h"  // NOLINT(build/include)
 #include "common_video/include/video_bitrate_allocator.h"
@@ -63,7 +62,7 @@ class VideoStreamEncoder : public VideoStreamEncoderInterface,
                      const VideoSendStream::Config::EncoderSettings& settings,
                      rtc::VideoSinkInterface<VideoFrame>* pre_encode_callback,
                      std::unique_ptr<OveruseFrameDetector> overuse_detector);
-  ~VideoStreamEncoder();
+  ~VideoStreamEncoder() override;
 
   void SetSource(rtc::VideoSourceInterface<VideoFrame>* source,
                  const DegradationPreference& degradation_preference) override;