modules/video_coding refactorings

The main purpose was the interface-> include rename, but other files
were also moved, eliminating the "main" dir.

To avoid breaking downstream, the "interface" directories were copied
into a new "video_coding/include" dir. The old headers got pragma
warnings added about deprecation (a very short deprecation since I plan
to remove them as soon downstream is updated).

Other files also moved:
video_coding/main/source -> video_coding
video_coding/main/test -> video_coding/test

BUG=webrtc:5095
TESTED=Passing compile-trybots with --clobber flag:
git cl try --clobber --bot=win_compile_rel --bot=linux_compile_rel --bot=android_compile_rel --bot=mac_compile_rel --bot=ios_rel --bot=linux_gn_rel --bot=win_x64_gn_rel --bot=mac_x64_gn_rel --bot=android_gn_rel -m tryserver.webrtc

R=stefan@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1417283007 .

Cr-Commit-Position: refs/heads/master@{#10694}
diff --git a/webrtc/modules/video_coding/video_coding.gypi b/webrtc/modules/video_coding/video_coding.gypi
index b292e0a..438d8f1 100644
--- a/webrtc/modules/video_coding/video_coding.gypi
+++ b/webrtc/modules/video_coding/video_coding.gypi
@@ -22,61 +22,61 @@
       ],
       'sources': [
         # interfaces
-        'main/interface/video_coding.h',
-        'main/interface/video_coding_defines.h',
+        'include/video_coding.h',
+        'include/video_coding_defines.h',
 
         # headers
-        'main/source/codec_database.h',
-        'main/source/codec_timer.h',
-        'main/source/content_metrics_processing.h',
-        'main/source/decoding_state.h',
-        'main/source/encoded_frame.h',
-        'main/source/fec_tables_xor.h',
-        'main/source/frame_buffer.h',
-        'main/source/generic_decoder.h',
-        'main/source/generic_encoder.h',
-        'main/source/inter_frame_delay.h',
-        'main/source/internal_defines.h',
-        'main/source/jitter_buffer.h',
-        'main/source/jitter_buffer_common.h',
-        'main/source/jitter_estimator.h',
-        'main/source/media_opt_util.h',
-        'main/source/media_optimization.h',
-        'main/source/nack_fec_tables.h',
-        'main/source/packet.h',
-        'main/source/qm_select_data.h',
-        'main/source/qm_select.h',
-        'main/source/receiver.h',
-        'main/source/rtt_filter.h',
-        'main/source/session_info.h',
-        'main/source/timestamp_map.h',
-        'main/source/timing.h',
-        'main/source/video_coding_impl.h',
+        'codec_database.h',
+        'codec_timer.h',
+        'content_metrics_processing.h',
+        'decoding_state.h',
+        'encoded_frame.h',
+        'fec_tables_xor.h',
+        'frame_buffer.h',
+        'generic_decoder.h',
+        'generic_encoder.h',
+        'inter_frame_delay.h',
+        'internal_defines.h',
+        'jitter_buffer.h',
+        'jitter_buffer_common.h',
+        'jitter_estimator.h',
+        'media_opt_util.h',
+        'media_optimization.h',
+        'nack_fec_tables.h',
+        'packet.h',
+        'qm_select_data.h',
+        'qm_select.h',
+        'receiver.h',
+        'rtt_filter.h',
+        'session_info.h',
+        'timestamp_map.h',
+        'timing.h',
+        'video_coding_impl.h',
 
         # sources
-        'main/source/codec_database.cc',
-        'main/source/codec_timer.cc',
-        'main/source/content_metrics_processing.cc',
-        'main/source/decoding_state.cc',
-        'main/source/encoded_frame.cc',
-        'main/source/frame_buffer.cc',
-        'main/source/generic_decoder.cc',
-        'main/source/generic_encoder.cc',
-        'main/source/inter_frame_delay.cc',
-        'main/source/jitter_buffer.cc',
-        'main/source/jitter_estimator.cc',
-        'main/source/media_opt_util.cc',
-        'main/source/media_optimization.cc',
-        'main/source/packet.cc',
-        'main/source/qm_select.cc',
-        'main/source/receiver.cc',
-        'main/source/rtt_filter.cc',
-        'main/source/session_info.cc',
-        'main/source/timestamp_map.cc',
-        'main/source/timing.cc',
-        'main/source/video_coding_impl.cc',
-        'main/source/video_sender.cc',
-        'main/source/video_receiver.cc',
+        'codec_database.cc',
+        'codec_timer.cc',
+        'content_metrics_processing.cc',
+        'decoding_state.cc',
+        'encoded_frame.cc',
+        'frame_buffer.cc',
+        'generic_decoder.cc',
+        'generic_encoder.cc',
+        'inter_frame_delay.cc',
+        'jitter_buffer.cc',
+        'jitter_estimator.cc',
+        'media_opt_util.cc',
+        'media_optimization.cc',
+        'packet.cc',
+        'qm_select.cc',
+        'receiver.cc',
+        'rtt_filter.cc',
+        'session_info.cc',
+        'timestamp_map.cc',
+        'timing.cc',
+        'video_coding_impl.cc',
+        'video_sender.cc',
+        'video_receiver.cc',
       ], # source
       # TODO(jschuh): Bug 1348: fix size_t to int truncations.
       'msvs_disabled_warnings': [ 4267, ],