Robustification of the echo suppression behavior during headset usage.

This CL robustifies the echo removal behavior when headsets are used.
In particular it:
-Introduces a secondary, more refined alignment when no alignment can
be found using the delay estimator.
-Changes decision logic for when to use the linear filter output.
-Changes the decision logic for when to be transparent.
-Changes the way that the transparent mode works.
-Makes the nonlinear mode less aggressive.
-Removes the detector for non-audible echoes.
-Makes the attenuation when there are signals with strong narrowband
characteristics more mild in scenarios with low render.

Furthermore the CL:
-Removes the input of external echo leakage information.


Bug: webrtc:9047,chromium:824111,webrtc:8314,webrtc:8671,webrtc:5201,webrtc:5919
Change-Id: Ied1fe0c0a35d3c31b47606ed2db319a73644d406
Reviewed-on: https://webrtc-review.googlesource.com/60866
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22548}

modules/audio_processing/aec3/render_delay_buffer.h

@@ -57,7 +57,7 @@ class RenderDelayBuffer {
   virtual bool SetDelay(size_t delay) = 0;
 
   // Gets the buffer delay.
-  virtual rtc::Optional<size_t> Delay() const = 0;
+  virtual size_t Delay() const = 0;
 
   // Gets the buffer delay.
   virtual size_t MaxDelay() const = 0;