feat: expose rtc video value (#30)

It looks like the video track is sometimes rotated internally.
Without access to rotation or the computed aspectRatio, it's
difficult to know the actual size of the video

Author: holzgeist

lib/src/rtc_video_renderer.dart

@@ -54,6 +54,8 @@ abstract class VideoRenderer {
 
   int get videoHeight;
 
+  RTCVideoValue get videoValue;
+
   bool get muted;
   set muted(bool mute);