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}

call/rtp_payload_params.h

@@ -15,6 +15,7 @@
 #include <vector>
 
 #include "api/video_codecs/video_encoder.h"
+#include "call/rtp_config.h"
 #include "common_types.h"  // NOLINT(build/include)
 #include "modules/rtp_rtcp/source/rtp_video_header.h"
 
@@ -23,12 +24,6 @@ namespace webrtc {
 class RTPFragmentationHeader;
 class RtpRtcp;
 
-// Currently only VP8/VP9 specific.
-struct RtpPayloadState {
-  int16_t picture_id = -1;
-  uint8_t tl0_pic_idx = 0;
-};
-
 // State for setting picture id and tl0 pic idx, for VP8 and VP9
 // TODO(nisse): Make these properties not codec specific.
 class RtpPayloadParams final {