Move AudioOptions to its own header file and target.

It is part of our api.

With the intention to later delete the inclusion of mediachannel.h from
api/peerconnectioninterface.h, and eliminate circular dependencies.

Bug: webrtc:7504
Change-Id: If44efd14d85675530e457760a1c4a1d338f931b7
Reviewed-on: https://webrtc-review.googlesource.com/41281
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21694}
diff --git a/api/peerconnectioninterface.h b/api/peerconnectioninterface.h
index f6fae58..0f8804a 100644
--- a/api/peerconnectioninterface.h
+++ b/api/peerconnectioninterface.h
@@ -78,6 +78,7 @@
 
 #include "api/audio_codecs/audio_decoder_factory.h"
 #include "api/audio_codecs/audio_encoder_factory.h"
+#include "api/audio_options.h"
 #include "api/datachannelinterface.h"
 #include "api/dtmfsenderinterface.h"
 #include "api/jsep.h"