@ character is dropped when setting the name property of Nodes

[dilettante54]

Godot version:
3.2.3

OS/device including version:
Windows 10

Issue description:
If you add a new node via add_child(), unless legible_unique_name is true, the new node has a few @ characters in the name.
If you then store the name property of the node in a variable, then set the node's name from the variable, Godot drops the @.
As far as I could tell, this isn't mentioned in the documentation. I ran into this issue when saving / loading scenes with children added on the fly and trying to reparent children to the proper parent nodes when loading.

Steps to reproduce:
As above.

Minimal reproduction project:
NameTest.zip

[Calinou]

Duplicate of #27608. This is now documented (it will be in the editor help in 3.3): #42865