Deprecate PeerConnectionFactory#createVideoSource(VideoCapturer).

This is done in preparation of moving VideoCapturer out of
video_api_java. Clients should update to using
createVideoSource(boolean).

CapturerObserver is moved to a separate file because it needs to stay
in video_api_java to allow VideoSource to depend on it.

Bug: webrtc:9496
Change-Id: I3c93f6bc4df553919dcbe05b00ef4c68f2c9ab60
Reviewed-on: https://webrtc-review.googlesource.com/87305
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23868}

sdk/android/api/org/webrtc/PeerConnectionFactory.java

@@ -357,6 +357,7 @@ public class PeerConnectionFactory {
     return new VideoSource(nativeCreateVideoSource(nativeFactory, isScreencast));
   }
 
+  @Deprecated
   public VideoSource createVideoSource(VideoCapturer capturer) {
     final EglBase.Context eglContext =
         localEglbase == null ? null : localEglbase.getEglBaseContext();