Add replacement interface for webrtc::GainConrol

The pointer-to-submodule interfaces are being removed.
This CL:
1) introduces AudioProcessing::Config::GainController1 with most config,
2) adds functions to APM for setting and getting analog gain,
3) creates a temporary GainControlConfigProxy to support the transition
   to the new config.
4) Moves the lock references in GainControlForExperimentalAgc and
   GainControlImpl into the GainControlConfigProxy, as it becomes the
   sole AGC object with functionality exposed to the client.

Bug: webrtc:9947, webrtc:9878
Change-Id: Ic31e15e9bb26d6497a92b77874e0b6cab21ff2b2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/126485
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27316}

modules/audio_processing/include/gain_control.h

@@ -31,7 +31,7 @@ class GainControl {
   // When an analog mode is set, this should be called after |ProcessStream()|
   // to obtain the recommended new analog level for the audio HAL. It is the
   // users responsibility to apply this level.
-  virtual int stream_analog_level() = 0;
+  virtual int stream_analog_level() const = 0;
 
   enum Mode {
     // Adaptive mode intended for use if an analog volume control is available