Move NetEq headers to api/

This CL also introduces NetEqFactory and NetEqControllerFactory
interfaces, as well as several convenience classes for working with
them: DefaultNetEqFactory, DefaultNetEqControllerFactory and
CustomNetEqFactory.

Bug: webrtc:11005
Change-Id: I1e8fc5154636ac2aad1a856828f80a2a758ad392
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/156945
Commit-Queue: Ivo Creusen <ivoc@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29671}
diff --git a/modules/audio_coding/neteq/packet_buffer_unittest.cc b/modules/audio_coding/neteq/packet_buffer_unittest.cc
index 0b638bf..0aff955 100644
--- a/modules/audio_coding/neteq/packet_buffer_unittest.cc
+++ b/modules/audio_coding/neteq/packet_buffer_unittest.cc
@@ -15,10 +15,10 @@
 #include <memory>
 
 #include "api/audio_codecs/builtin_audio_decoder_factory.h"
+#include "api/neteq/tick_timer.h"
 #include "modules/audio_coding/neteq/mock/mock_decoder_database.h"
 #include "modules/audio_coding/neteq/mock/mock_statistics_calculator.h"
 #include "modules/audio_coding/neteq/packet.h"
-#include "modules/audio_coding/neteq/tick_timer.h"
 #include "test/gmock.h"
 #include "test/gtest.h"