Add core multi-channel pipeline in AEC3

This CL adds basic the basic pipeline to support multi-channel
processing in AEC3.

Apart from that, it removes the 8 kHz processing support in several
places of the AEC3 code.

Bug: webrtc:10913
Change-Id: If5b75fa325ed0071deea94a7546cb4a7adf22137
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150332
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29017}

api/audio/echo_canceller3_factory.cc

@@ -22,6 +22,17 @@ EchoCanceller3Factory::EchoCanceller3Factory(const EchoCanceller3Config& config)
     : config_(config) {}
 
 std::unique_ptr<EchoControl> EchoCanceller3Factory::Create(int sample_rate_hz) {
-  return absl::make_unique<EchoCanceller3>(config_, sample_rate_hz);
+  return absl::make_unique<EchoCanceller3>(config_, sample_rate_hz,
+                                           /*num_render_channels=*/1,
+                                           /*num_capture_channels=*/1);
 }
+
+std::unique_ptr<EchoControl> EchoCanceller3Factory::Create(
+    int sample_rate_hz,
+    size_t num_render_channels,
+    size_t num_capture_channels) {
+  return absl::make_unique<EchoCanceller3>(
+      config_, sample_rate_hz, num_render_channels, num_capture_channels);
+}
+
 }  // namespace webrtc

api/audio/echo_canceller3_factory.h

@@ -28,9 +28,16 @@ class RTC_EXPORT EchoCanceller3Factory : public EchoControlFactory {
   // configuration.
   explicit EchoCanceller3Factory(const EchoCanceller3Config& config);
 
-  // Creates an EchoCanceller3 running at the specified sampling rate.
+  // Creates an EchoCanceller3 running at the specified sampling rate using a
+  // mono setup
   std::unique_ptr<EchoControl> Create(int sample_rate_hz) override;
 
+  // Creates an EchoCanceller3 running at the specified sampling rate and a
+  // specified number of channels.
+  std::unique_ptr<EchoControl> Create(int sample_rate_hz,
+                                      size_t num_render_channels,
+                                      size_t num_capture_channels) override;
+
  private:
   const EchoCanceller3Config config_;
 };

api/audio/echo_control.h

@@ -48,6 +48,11 @@ class EchoControl {
 class EchoControlFactory {
  public:
   virtual std::unique_ptr<EchoControl> Create(int sample_rate_hz) = 0;
+  virtual std::unique_ptr<EchoControl> Create(int sample_rate_hz,
+                                              size_t num_render_channels,
+                                              size_t num_capture_channels) {
+    return Create(sample_rate_hz);
+  }
   virtual ~EchoControlFactory() = default;
 };
 }  // namespace webrtc