Custom userData refactor

Turned it into a map to make it actually useful so that multiple effects can exchange data

Author: Chman

PostProcessing/Runtime/PostProcessRenderContext.cs

@@ -1,3 +1,5 @@
+using System.Collections.Generic;
+
 namespace UnityEngine.Rendering.PostProcessing
 {
 #if UNITY_2017_2_OR_NEWER
@@ -75,10 +77,9 @@ public Camera camera
         // Property sheet factory handled by the currently active PostProcessLayer
         public PropertySheetFactory propertySheets { get; internal set; }
 
-        // Custom user data object (unused by builtin effects, feel free to store whatever you want
-        // in this object)
-        // TODO: Make this more useful
-        public object userData { get; set; }
+        // Custom user data objects (unused by builtin effects, feel free to store whatever you want
+        // in this dictionary)
+        public Dictionary<string, object> userData { get; private set; }
 
         // Reference to the internal debug layer
         public PostProcessDebugLayer debugLayer { get; internal set; }
@@ -136,6 +137,11 @@ public void Reset()
             autoExposureTexture = null;
             logLut = null;
             autoExposure = null;
+
+            if (userData == null)
+                userData = new Dictionary<string, object>();
+
+            userData.Clear();
         }
 
         // Checks if TAA is enabled & supported