Re-enable culling mask UI

This PR addresses [UUM-66079](https://jira.unity3d.com/browse/UUM-66079), and partially reverts some changes made in #43938, since @MINGWAI found a use-case where the Culling Mask is still useful in Forward+.

This change
1. edits the tooltip of the culling mask.
2. makes the Culling Mask always editable, regardless of Deferred, Forward, Forward+ etc.
3. If the culling mask is set to a non-default value, adds this info box to alleviate the source of lots of user confusion.

<img width="600" alt="image" src="https://media.github.cds.internal.unity3d.com/user/2726/files/04898627-06ec-4271-b411-10f1006707ee">

Author: ApoorvaJ

Packages/com.unity.render-pipelines.universal/Editor/Lighting/UniversalRenderPipelineLightUI.Drawers.cs

@@ -286,31 +286,10 @@ static void DrawRenderingContent(UniversalRenderPipelineSerializedLight serializ
                 }
             }
 
-            var rendererList = UniversalRenderPipeline.asset.rendererDataList;
-            bool hasNonForwardPlusRenderer = false;
-            foreach (var r in rendererList)
-            {
-                if (r is UniversalRendererData ur)
-                {
-                    if (ur.renderingMode != RenderingMode.ForwardPlus)
-                    {
-                        hasNonForwardPlusRenderer = true;
-                        break;
-                    }
-                }
-                else
-                {
-                    hasNonForwardPlusRenderer = true;
-                    break;
-                }
-            }
-
-            GUI.enabled = hasNonForwardPlusRenderer;
-            EditorGUILayout.PropertyField(serializedLight.settings.cullingMask, hasNonForwardPlusRenderer ? Styles.CullingMask : Styles.CullingMaskDisabled);
-            GUI.enabled = true;
+            EditorGUILayout.PropertyField(serializedLight.settings.cullingMask, Styles.CullingMask);
             if (serializedLight.settings.cullingMask.intValue != -1)
             {
-                EditorGUILayout.HelpBox(Styles.CullingMaskWarning.text, MessageType.Warning);
+                EditorGUILayout.HelpBox(Styles.CullingMaskWarning.text, MessageType.Info);
             }
         }
 

Packages/com.unity.render-pipelines.universal/Editor/Lighting/UniversalRenderPipelineLightUI.Skin.cs

@@ -21,9 +21,8 @@ private static class Styles
             public static readonly GUIContent BakingWarning = EditorGUIUtility.TrTextContent("Light mode is currently overridden to Realtime mode. Enable Baked Global Illumination to use Mixed or Baked light modes.");
             public static readonly GUIContent DisabledLightWarning = EditorGUIUtility.TrTextContent("Lighting has been disabled in at least one Scene view. Any changes applied to lights in the Scene will not be updated in these views until Lighting has been enabled again.");
             public static readonly GUIContent SunSourceWarning = EditorGUIUtility.TrTextContent("This light is set as the current Sun Source, which requires a directional light. Go to the Lighting Window's Environment settings to edit the Sun Source.");
-            public static readonly GUIContent CullingMask = EditorGUIUtility.TrTextContent("Culling Mask", "Specifies which layers will be affected or excluded from the light's effect on objects in the scene. This only applies to objects rendered using the Forward rendering path, and transparent objects rendered using the Deferred rendering path.\n\nUse Rendering Layers instead, which is supported across all rendering paths.");
-            public static readonly GUIContent CullingMaskDisabled = EditorGUIUtility.TrTextContent("Culling Mask", "Culling Mask is disabled. This is because all active renderers use the Forward+ rendering path, which doesn't support Culling Mask. Use Rendering Layers instead, which is supported across all rendering paths.");
-            public static readonly GUIContent CullingMaskWarning = EditorGUIUtility.TrTextContent("Culling Mask only works with Forward rendering. Instead, use Rendering Layers on the Light, and Rendering Layer Mask on the Mesh Renderer, which will work across Deferred, Forward, and Forward+ rendering.");
+            public static readonly GUIContent CullingMask = EditorGUIUtility.TrTextContent("Culling Mask", "Specifies which lights are culled per camera. To control exclude certain lights affecting certain objects, use Rendering Layers instead, which is supported across all rendering paths.");
+            public static readonly GUIContent CullingMaskWarning = EditorGUIUtility.TrTextContent("Culling Mask should be used to control which lights are culled per camera. If you want to exclude certain lights from affecting certain objects, use Rendering Layers on the Light, and Rendering Layer Mask on the Mesh Renderer.");
 
             public static readonly GUIContent ShadowRealtimeSettings = EditorGUIUtility.TrTextContent("Realtime Shadows", "Settings for realtime direct shadows.");
             public static readonly GUIContent ShadowStrength = EditorGUIUtility.TrTextContent("Strength", "Controls how dark the shadows cast by the light will be.");