Reland "Add ability to state whether the APM output will be used"

This is a reland of 8be2f201ba8790501f6f3fa39f00017f02fca46d

Original change's description:
> Add ability to state whether the APM output will be used
> 
> This CL adds the ability for the surrounding code to state that the
> APM output will not be used. The intended usecase for this is to allow
> APM to run at a lower complexity when the endpoint is muted.
> When APM has been informed that the output will not be used, it can
> turn off code that is needed only for ensuring that the output audio
> will sound good.
> 
> Bug: b/154437967,b/163802450
> Change-Id: I8e22989e35354372e96191d15da44beb9d1b26ae
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/181200
> Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
> Commit-Queue: Per Åhgren <peah@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#31949}

Bug: b/154437967
Bug: b/163802450
Change-Id: Ia77a9e43f913929d1afa72212f1ea6c192d0e519
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/181887
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Commit-Queue: Per Åhgren <peah@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31957}
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index d84318f..9e2d6dc 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -384,7 +384,8 @@
       kCaptureFixedPostGain,
       kPlayoutVolumeChange,
       kCustomRenderProcessingRuntimeSetting,
-      kPlayoutAudioDeviceChange
+      kPlayoutAudioDeviceChange,
+      kCaptureOutputUsed
     };
 
     // Play-out audio device properties.
@@ -434,6 +435,10 @@
       return {Type::kCustomRenderProcessingRuntimeSetting, payload};
     }
 
+    static RuntimeSetting CreateCaptureOutputUsedSetting(bool payload) {
+      return {Type::kCaptureOutputUsed, payload};
+    }
+
     Type type() const { return type_; }
     // Getters do not return a value but instead modify the argument to protect
     // from implicit casting.
@@ -445,6 +450,10 @@
       RTC_DCHECK(value);
       *value = value_.int_value;
     }
+    void GetBool(bool* value) const {
+      RTC_DCHECK(value);
+      *value = value_.bool_value;
+    }
     void GetPlayoutAudioDeviceInfo(PlayoutAudioDeviceInfo* value) const {
       RTC_DCHECK(value);
       *value = value_.playout_audio_device_info;
@@ -463,6 +472,7 @@
       U(PlayoutAudioDeviceInfo value) : playout_audio_device_info(value) {}
       float float_value;
       int int_value;
+      bool bool_value;
       PlayoutAudioDeviceInfo playout_audio_device_info;
     } value_;
   };