Fix hide internal components in Unity 6:

- [AddComponentMenu("")] does not work in Unity 6.
- Replace it with [AddComponentMenu("/")]
- This alternative is confirmed to also work in Unity 2022.

Runtime/Activator.cs

@@ -19,7 +19,7 @@ namespace nadena.dev.modular_avatar.core
     /// initially inactive in the scene (which can have high overhead if the user has a lot of inactive avatars in the
     /// scene).
     /// </summary>
-    [AddComponentMenu("")]
+    [AddComponentMenu("/")]
     [ExecuteInEditMode]
     [DefaultExecutionOrder(-9998)]
     public class Activator : MonoBehaviour, IEditorOnly
@@ -30,7 +30,7 @@ namespace nadena.dev.modular_avatar.core
         }
     }
 
-    [AddComponentMenu("")]
+    [AddComponentMenu("/")]
     [ExecuteInEditMode]
     [DefaultExecutionOrder(-9997)]
     public class AvatarActivator : MonoBehaviour, IEditorOnly

Runtime/ModularAvatarConvertConstraints.cs

@@ -6,7 +6,7 @@ namespace nadena.dev.modular_avatar.core
 #if MA_VRCSDK3_AVATARS
     [AddComponentMenu("Modular Avatar/MA Convert Constraints")]
 #else
-    [AddComponentMenu("")]
+    [AddComponentMenu("/")]
 #endif
     [HelpURL("https://modular-avatar.nadena.dev/docs/reference/convert-constraints?lang=auto")]
     public class ModularAvatarConvertConstraints : AvatarTagComponent