feat: Added BlendTree to right click create asset menu. (#555)

* Added BlendTree to right click create asset menu.

Not sure where to put it, so into the root editor folder it goes.

* Update CreateBlendTree.cs

* chore: add missing .meta file

---------

Co-authored-by: bd_ <bd_@nadena.dev>

Editor/CreateBlendTree.cs

@@ -0,0 +1,32 @@
+using System.IO;
+using UnityEditor;
+using UnityEditor.Animations;
+using UnityEditor.ProjectWindowCallback;
+using UnityEngine;
+
+namespace nadena.dev.modular_avatar.core.editor
+{
+    internal static class CreateBlendTree
+    {
+        [MenuItem("Assets/Create/BlendTree", priority = 411)]
+        static void CreateNewBlendTree()
+        {
+            ProjectWindowUtil.StartNameEditingIfProjectWindowExists(
+               0,
+               Editor.CreateInstance<DoCreateBlendTree>(),
+               "New BlendTree.asset",
+               EditorGUIUtility.IconContent("BlendTree Icon").image as Texture2D,
+               null);
+        }
+
+        class DoCreateBlendTree : EndNameEditAction
+        {
+            public override void Action(int instanceId, string pathName, string resourceFile)
+            {
+                BlendTree blendTree = new BlendTree { name = Path.GetFileNameWithoutExtension(pathName) };
+                AssetDatabase.CreateAsset(blendTree, pathName);
+                Selection.activeObject = blendTree;
+            }
+        }
+    }
+}

Editor/CreateBlendTree.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: e608a27c3d14edf43858004513948da1
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: