Allow mods to control how looped sounds are used.

OpenRA.Platforms.Default/DummySoundEngine.cs

@@ -57,6 +57,7 @@ namespace OpenRA.Platforms.Default
 		public void StopAllSounds() { }
 		public void SetListenerPosition(WPos position) { }
 		public void SetSoundLooping(bool looping, ISound sound) { }
+		public void SetSoundPosition(ISound sound, WPos position) { }
 		public void Dispose() { }
 	}
 

OpenRA.Platforms.Default/OpenAlSoundEngine.cs

@@ -350,6 +350,11 @@ namespace OpenRA.Platforms.Default
 			((OpenAlSound)sound)?.SetLooping(looping);
 		}
 
+		public void SetSoundPosition(ISound sound, WPos position)
+		{
+			((OpenAlSound)sound)?.SetPosition(position);
+		}
+
 		~OpenAlSoundEngine()
 		{
 			Dispose(false);