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

livekit/src/room/participant/local_participant.rs

@@ -31,6 +31,8 @@ impl LocalParticipant {
         }
     }
 
+    pub async fn publish_track(&self) {}
+
     pub async fn publish_data(
         &self,
         data: &[u8],