APM: rename `AnalogGainStatsReporter` to `InputVolumeStatsReporter`

Adopt the new naming convention, which replaces "analog gain" and
"mic level" with "input volume", in the input volume stats reporter.

Bug: webrtc:7494
Change-Id: Ia24876151f51dd1dcc4e4f9db56c64d11ae3b442
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/279840
Reviewed-by: Hanna Silen <silen@webrtc.org>
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38467}
diff --git a/modules/audio_processing/audio_processing_impl.cc b/modules/audio_processing/audio_processing_impl.cc
index 1d588fe..76e3804 100644
--- a/modules/audio_processing/audio_processing_impl.cc
+++ b/modules/audio_processing/audio_processing_impl.cc
@@ -1131,8 +1131,7 @@
   }
 
   if (capture_.applied_input_volume.has_value()) {
-    // Log the applied input volume only when available.
-    input_volume_stats_reporter_.UpdateStatistics(
+    applied_input_volume_stats_reporter_.UpdateStatistics(
         *capture_.applied_input_volume);
   }