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/include/livekit/rtc_error.h

@@ -2,13 +2,11 @@
 // Created by theom on 04/09/2022.
 //
 
-#ifndef CLIENT_SDK_NATIVE_RTC_ERROR_H
-#define CLIENT_SDK_NATIVE_RTC_ERROR_H
+#pragma once
 
 #include "api/rtc_error.h"
-#include "webrtc-sys/src/rtc_error.rs.h"
 #include "rust/cxx.h"
-#include "rust_types.h"
+#include "webrtc-sys/src/rtc_error.rs.h"
 
 namespace livekit {
 
@@ -22,5 +20,3 @@ void throw_error();
 #endif
 
 }  // namespace livekit
-
-#endif  // CLIENT_SDK_NATIVE_RTC_ERROR_H