Remove extra NOTIFICATION_VISIBILITY_CHANGED notifications in docks

[lodetrick]

See #113034 (comment)
Related: #113024

When upgrading docks to the new system, I first noticed that docks treated the NOTIFICATION_{ENTER, EXIT}_TREE like constructors and destructors, only being called once. When they used the EditorBottomPanel, this was valid, but now that they use the EditorDockManager, this is no longer true. Thus, any actions that must be done once, should be moved.

In #113034 (comment), the underlying bug was a case where NOTIFICATION_VISIBILITY_CHANGED was used to know when the panel was enabled or disabled. This is valid if the notification only happened when both the enabled and visible, and disabled and not visible. However, due to an ordering issue with EditorDockManager, the NOTIFICATION_VISIBILITY_CHANGED(true) was emitted when closing the dock, and NOTIFICATION_VISIBILITY_CHANGED(false) was emitted when opening the dock, leading to incorrect assumptions.

This PR swaps the order of operations so that the notification is only emitted correctly, to preserve assumptions. This has the benefit of removing unnecessary operations when opening and closing docks.

	EditorDock::open()	EditorDock::close()
Before:	NOTIFICATION_VISIBILITY_CHANGED NOTIFICATION_EXIT_TREE NOTIFICATION_VISIBILITY_CHANGED NOTIFICATION_ENTER_TREE NOTIFICATION_VISIBILITY_CHANGED NOTIFICATION_VISIBILITY_CHANGED	NOTIFICATION_EXIT_TREE NOTIFICATION_VISIBILITY_CHANGED NOTIFICATION_ENTER_TREE NOTIFICATION_VISIBILITY_CHANGED
After:	NOTIFICATION_EXIT_TREE NOTIFICATION_ENTER_TREE NOTIFICATION_VISIBILITY_CHANGED	NOTIFICATION_VISIBILITY_CHANGED NOTIFICATION_EXIT_TREE NOTIFICATION_ENTER_TREE

[KoBeWi]

Something bad is happening when you close Scene dock in right UR slot:

godot.windows.editor.dev.x86_64_ygLeHgtF2d.mp4

It's somewhat reproducible without this PR, but it's not as extreme.

[KoBeWi]

I realized a major flaw in EditorDockManager. closed_dock_parent is not invisible. If it was, this problem wouldn't exist and the order of making things invisible wouldn't matter, because nodes reparented to closed dock parent couldn't become visible. We should still hide them though, so is_visible() is false.

[lodetrick]

I made it so that the closed_dock_parent is a new hidden control under the gui_base.

When testing I came across this error when I clicked Editor -> Editor Layout -> Default but I was able to reproduce it in master so I don't think its related.

ERROR: The active_submenu_index should never be -1 when _submenu_hidden is entered.
   at: _submenu_hidden (scene/gui/popup_menu.cpp:2242)

Edit: Nevermind it's happening when you stop hovering over a menu item so very unrelated

[Repiteo]

Thanks!