Block Canvas: Reuse saved block scene resource

By simply assigning it to the scene resource property when loading the
tree.

Follow up of 01ab76c which already removed all resource regeneration
except when loading the canvas.

Author: manuq

addons/block_code/ui/block_canvas/block_canvas.gd

@@ -164,6 +164,7 @@ func load_tree(parent: Node, node: SerializedBlockTreeNode):
 	var scene: Block = load(_block_scene_path).instantiate()
 	for prop_pair in node.serialized_block.serialized_props:
 		scene.set(prop_pair[0], prop_pair[1])
+	scene.resource = node
 	parent.add_child(scene)
 
 	var scene_block: Block = scene as Block