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* Remove some outdated comment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/FixedPointHelper.cs

@@ -16,6 +16,12 @@ namespace Ryujinx.Audio.Renderer.Dsp
             return (float)value / (1 << qBits);
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static float ConvertFloat(float value, int qBits)
+        {
+            return value / (1 << qBits);
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static int ToFixed(float value, int qBits)
         {