amadeus: Add missing compressor effect from REV11 (#4010)

* amadeus: Add missing compressor effect from REV11

This was in my reversing notes but seems I completely forgot to
implement it

Also took the opportunity to simplify the Limiter effect a bit.

* Remove some outdated comment

* Address gdkchan's comments

Ryujinx.Audio/Renderer/Dsp/Effect/ExponentialMovingAverage.cs

@@ -0,0 +1,26 @@
+using System.Runtime.CompilerServices;
+
+namespace Ryujinx.Audio.Renderer.Dsp.Effect
+{
+    public struct ExponentialMovingAverage
+    {
+        private float _mean;
+
+        public ExponentialMovingAverage(float mean)
+        {
+            _mean = mean;
+        }
+
+        public float Read()
+        {
+            return _mean;
+        }
+
+        public float Update(float value, float alpha)
+        {
+            _mean += alpha * (value - _mean);
+
+            return _mean;
+        }
+    }
+}