Move AudioDecoder and related stuff to the api/ directory

BUG=webrtc:5805, webrtc:6725

Review-Url: https://codereview.webrtc.org/2668523004
Cr-Commit-Position: refs/heads/master@{#16534}
diff --git a/webrtc/logging/BUILD.gn b/webrtc/logging/BUILD.gn
index 3684381..52d421e 100644
--- a/webrtc/logging/BUILD.gn
+++ b/webrtc/logging/BUILD.gn
@@ -139,7 +139,7 @@
         "../base:rtc_base_approved",
 
         # TODO(kwiberg): Remove this dependency.
-        "../modules/audio_coding:audio_format",
+        "../api/audio_codecs:audio_codecs_api",
         "../modules/rtp_rtcp:rtp_rtcp",
         "//third_party/gflags",
       ]