fix: datachannel deadlocks & dispose crashes (#87)

- Fix datachannel deadlock on dispose
- Fix audio device being disposed on the wrong thread
- Allow multiple RtcRuntime to be created (Useful for unit tests where we use multiple PeerConnectionFactory)

webrtc-sys/include/livekit/peer_connection_factory.h

@@ -17,6 +17,8 @@
 #pragma once
 
 #include "api/peer_connection_interface.h"
+#include "api/scoped_refptr.h"
+#include "livekit/audio_device.h"
 #include "media_stream.h"
 #include "peer_connection.h"
 #include "rtp_parameters.h"
@@ -57,6 +59,7 @@ class PeerConnectionFactory {
 
  private:
   std::shared_ptr<RtcRuntime> rtc_runtime_;
+  rtc::scoped_refptr<AudioDevice> audio_device_;
   rtc::scoped_refptr<webrtc::PeerConnectionFactoryInterface> peer_factory_;
 };