Transform lock is not saved for scenes instanced in editor

[kubecz3k]

Operating system or device, Godot version, GPU Model and driver (if graphics related):
35e7f99

Issue description:
When setting transform lock on subscene and saving the scene the lock should be saved as well. Unfortunately that's not the case:

Saving the lock works well for 'normal' (not subscene) nodes.

Steps to reproduce:

1. Create scene with node2d as root. Save it as Scene2D
2. Create another scene, add some node, instance Scene2D in editor as child of that node.
3. Set transform lock on Scene2D
4. Save the scene
5. Close and reopen the scene

Link to minimal example project:

[kubecz3k]

Lock information is stored in node metadata (node.set_meta("_edit_lock_", true);).
I was looking at EditorNode::_save_scene in order to find why this metadata is not saved in case of instanced subscenes. But without luck so far. If someone know what need to be done in order to make it work I would be obligated for some info.
update: According to #12359 (comment) metadata should not be stored in file, it should be put in file as properties.

[AndHalfAFish]

I'm having the same problem in Godot 3.2.1.stable (3d project).

[KoBeWi]

This was half-fixed by #59452
You can add a lock to instanced scene, but if the original scene is already locked, you can't remove it.