Reworked backbuffer transfer function parameter into a clearly designated enum

Runtime/OpticalFlow/OpticalFlow.cs

@@ -39,10 +39,18 @@ namespace FidelityFX.OpticalFlow
             public ResourceView OpticalFlowVector;
             public ResourceView OpticalFlowSCD;
             public bool Reset;
-            public int BackbufferTransferFunction;
+            
+            public BackbufferTransferFunction BackbufferTransferFunction;
             public Vector2 MinMaxLuminance;
         }
 
+        public enum BackbufferTransferFunction
+        {
+            LDR_sRGB,
+            HDR_PQ,
+            HDR_scRGB,
+        }
+
         public static Vector2Int GetOpticalFlowTextureSize(Vector2Int displaySize)
         {
             return GetOpticalFlowTextureSize(displaySize, MinBlockSize);