Move congestion controller to a separate module.

This allows other projects to more easily depend on this.

The plan is to move remote_bitrate_estimator and bitrate_controller into this module and reduce the exposed interface to only a simplified version of congestion_controller.h.

No functional changes in this CL.

R=mflodman@webrtc.org, pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1718473002 .

Cr-Commit-Position: refs/heads/master@{#11718}
diff --git a/webrtc/modules/modules.gyp b/webrtc/modules/modules.gyp
index 683b355..d520156 100644
--- a/webrtc/modules/modules.gyp
+++ b/webrtc/modules/modules.gyp
@@ -14,6 +14,7 @@
     'audio_device/audio_device.gypi',
     'audio_processing/audio_processing.gypi',
     'bitrate_controller/bitrate_controller.gypi',
+    'congestion_controller/congestion_controller.gypi',
     'desktop_capture/desktop_capture.gypi',
     'media_file/media_file.gypi',
     'pacing/pacing.gypi',