Correct and soften the AEC3 handling of saturated mic signals

This CL changes the handling of saturated microphone signals in AEC3.

Some of the changes included are
-Make the detection of saturated echoes depend on the echo path gain
 estimate.
-Remove redundant code related to echo saturation.
-Correct the computation of residual echoes when the echo is saturated.
-Soften the echo removal during echo saturation.

Bug: webrtc:9119
Change-Id: I5cb11cd449de552ab670beeb24ed8112f8beb734
Reviewed-on: https://webrtc-review.googlesource.com/67220
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22809}

api/audio/echo_canceller3_config.h

@@ -62,9 +62,9 @@ struct EchoCanceller3Config {
   } erle;
 
   struct EpStrength {
-    float lf = 2.f;
-    float mf = 2.f;
-    float hf = 2.f;
+    float lf = 10.f;
+    float mf = 10.f;
+    float hf = 10.f;
     float default_len = 0.f;
     bool echo_can_saturate = true;
     bool bounded_erl = false;