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/rtc_tools/BUILD.gn b/rtc_tools/BUILD.gn
index 5a8ffc3..fb9f885 100644
--- a/rtc_tools/BUILD.gn
+++ b/rtc_tools/BUILD.gn
@@ -324,6 +324,7 @@
       defines = [ "ENABLE_RTC_EVENT_LOG" ]
       deps = [
         ":event_log_visualizer_utils",
+        "../api/neteq:neteq_api",
         "../api/rtc_event_log",
         "../logging:rtc_event_log_parser",
         "../modules/audio_coding:neteq",