New file api/video/BUILD.gn

Build targets involving files under api/video/ are moved into this
file, from api/BUILD.gn. In addition, drop "_api" part of target
names, and move the header file api/videosinkinterface.h to
api/video/video_sink_interface.h.

Bug: webrtc:9253
Change-Id: I2896d3f063db8dff902bc29738578395b2fcc155
Reviewed-on: https://webrtc-review.googlesource.com/75500
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23207}
diff --git a/api/mediastreaminterface.h b/api/mediastreaminterface.h
index 2e2cff0..34a3143 100644
--- a/api/mediastreaminterface.h
+++ b/api/mediastreaminterface.h
@@ -27,7 +27,7 @@
 // TODO(zhihuang): Remove unrelated headers once downstream applications stop
 // relying on them; they were previously transitively included by
 // mediachannel.h, which is no longer a dependency of this file.
-#include "api/videosinkinterface.h"
+#include "api/video/video_sink_interface.h"
 #include "api/videosourceinterface.h"
 #include "modules/audio_processing/include/audio_processing_statistics.h"
 #include "rtc_base/ratetracker.h"