Move video_encoder.h and video_decoder.h to /api and create GN targets for them

webrtc/test/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../webrtc.gni")
 import("//build/config/ui.gni")
@@ skipping 383 matching lines @@
     suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
   }
 
   deps = [
     ":direct_transport",
     ":fake_audio_device",
     ":rtp_test_utils",
     ":test_support",
     ":video_test_common",
     "..:webrtc_common",
+    "../api/video_codecs:video_codecs_api",
     "../audio",
     "../base:rtc_base_approved",
     "../call",
     "../modules/audio_mixer:audio_mixer_impl",
     "../modules/audio_processing",
     "../video",
     "//testing/gmock",
     "//testing/gtest",
   ]
   if (!is_android) {
@@ skipping 65 matching lines @@
     # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
     suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
   }
 
   deps = [
     ":test_support",
     "../modules/media_file",
     "//testing/gtest",
   ]
 }