Added a define symbol to player settings for v2

UNITY_POST_PROCESSING_STACK_V2 is now available to users & asset creators

Author: Chman

PostProcessing/Editor/Tools/DefineSetter.cs

@@ -0,0 +1,28 @@
+using System.Linq;
+
+namespace UnityEditor.Rendering.PostProcessing
+{
+    [InitializeOnLoad]
+    sealed class DefineSetter
+    {
+        const string k_Define = "UNITY_POST_PROCESSING_STACK_V2";
+        
+        static DefineSetter()
+        {
+            var target = EditorUserBuildSettings.selectedBuildTargetGroup;
+            var defines = PlayerSettings.GetScriptingDefineSymbolsForGroup(target).Trim();
+
+            var list = defines.Split(';', ' ')
+                .Where(x => !string.IsNullOrEmpty(x))
+                .ToList();
+
+            if (list.Contains(k_Define))
+                return;
+
+            list.Add(k_Define);
+            defines = list.Aggregate((a, b) => a + ";" + b);
+
+            PlayerSettings.SetScriptingDefineSymbolsForGroup(target, defines);
+        }
+    }
+}