RtpTransceiver bindings & requirements for publishing tracks (#39)

- RtpSender
- RtpReceiver
- RtpTransceiver
- RtpParameters
- VideoFrameBuilder
- Interior mutability on c++ side
- Cleanup bindings ( Use #pragma once instead of include guards )
     - webrtc-sys/src/* headers are now used in only one place 
     - Avoid confusion between generated headers and our headers
- AdaptedVideoTrackSource
- Cleanup the workaround with unsupported Vec<Shared<T>>
    - Put everything inside one file

webrtc-sys/src/video_frame.cpp

@@ -0,0 +1,74 @@
+#include "livekit/video_frame.h"
+
+#include <memory>
+
+#include "api/video/video_frame.h"
+
+namespace livekit {
+VideoFrame::VideoFrame(const webrtc::VideoFrame& frame)
+    : frame_(std::move(frame)) {}
+
+int VideoFrame::width() const {
+  return frame_.width();
+}
+int VideoFrame::height() const {
+  return frame_.height();
+}
+uint32_t VideoFrame::size() const {
+  return frame_.size();
+}
+uint16_t VideoFrame::id() const {
+  return frame_.id();
+}
+int64_t VideoFrame::timestamp_us() const {
+  return frame_.timestamp_us();
+}
+int64_t VideoFrame::ntp_time_ms() const {
+  return frame_.ntp_time_ms();
+}
+uint32_t VideoFrame::transport_frame_id() const {
+  return frame_.transport_frame_id();
+}
+uint32_t VideoFrame::timestamp() const {
+  return frame_.timestamp();
+}
+
+VideoRotation VideoFrame::rotation() const {
+  return static_cast<VideoRotation>(frame_.rotation());
+}
+
+// TODO(theomonnom) This shouldn't create a new shared_ptr at each call
+std::unique_ptr<VideoFrameBuffer> VideoFrame::video_frame_buffer() const {
+  return std::make_unique<VideoFrameBuffer>(frame_.video_frame_buffer());
+}
+
+webrtc::VideoFrame VideoFrame::get() const {
+  return frame_;
+}
+
+void VideoFrameBuilder::set_video_frame_buffer(
+    std::unique_ptr<VideoFrameBuffer> buffer) {
+  builder_.set_video_frame_buffer(buffer->get());
+}
+
+void VideoFrameBuilder::set_timestamp_us(int64_t timestamp_us) {
+  builder_.set_timestamp_us(timestamp_us);
+}
+
+void VideoFrameBuilder::set_rotation(VideoRotation rotation) {
+  builder_.set_rotation(static_cast<webrtc::VideoRotation>(rotation));
+}
+
+void VideoFrameBuilder::set_id(uint16_t id) {
+  builder_.set_id(id);
+}
+
+std::unique_ptr<VideoFrame> VideoFrameBuilder::build() {
+  return std::make_unique<VideoFrame>(builder_.build());
+}
+
+std::unique_ptr<VideoFrameBuilder> create_video_frame_builder() {
+  return std::make_unique<VideoFrameBuilder>();
+}
+
+}  // namespace livekit