Changed AssetsHelpers from editor window to context menu workflow.

Editor/AssetsHelpers/Helpers/AssetCreationHelpers.cs

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+using UnityEditor;
+using UnityEngine;
+using UnityEngine.Rendering.HighDefinition;
+
+namespace Misaki.ArtToolEditor
+{
+    public static class AssetCreationHelpers
+    {
+        public static GameObject CreateDecal(string path)
+        {
+            var decal = new GameObject("Temp_Decal");
+            decal.AddComponent<DecalProjector>();
+            PrefabUtility.SaveAsPrefabAsset(decal, path);
+            Object.DestroyImmediate(decal);
+            return AssetDatabase.LoadAssetAtPath<GameObject>(path);
+        }
+    }
+}

Editor/AssetsHelpers/Helpers/AssetCreationHelpers.cs.meta

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+fileFormatVersion: 2
+guid: 4e43fc7bacddd9a46ba17e461058fc90