Add XRToolsViewport2DIn3D script name. (GodotVR#661)

addons/godot-xr-tools/objects/viewport_2d_in_3d.gd

@@ -1,4 +1,5 @@
 @tool
+class_name XRToolsViewport2DIn3D
 extends Node3D
 
 
@@ -121,6 +122,11 @@ var _screen_material : StandardMaterial3D
 var _dirty := _DIRTY_ALL
 
 
+# Add support for is_xr_class on XRTools classes
+func is_xr_class(p_name : String) -> bool:
+	return p_name == "XRToolsViewport2DIn3D"
+
+
 # Called when the node enters the scene tree for the first time.
 func _ready():
 	is_ready = true