Move VideoFrame and related declarations to webrtc/api/video.

Moves webrtc/common_video/rotation.h and parts of
webrtc/common_video/include/video_frame_buffer.h and
webrtc/video_frame.h, and adds to a new GN target api:video_frame_api.

BUG=webrtc:5880

Review-Url: https://codereview.webrtc.org/2517173004
Cr-Commit-Position: refs/heads/master@{#15993}

webrtc/modules/video_coding/include/video_coding_defines.h

@@ -14,8 +14,10 @@
 #include <string>
 #include <vector>
 
+#include "webrtc/api/video/video_frame.h"
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/typedefs.h"
+// For EncodedImage
 #include "webrtc/video_frame.h"
 
 namespace webrtc {