Using "Use Native File Dialogs" does not add file suffixes

[DancingEngie]

The problem

Describe the bug
There is an option in Godot's editor settings to use the system's own file explorer to save or load files in place of Godot's. It's called "Use Native File Dialogues".
I noticed that new timelines and styles mysteriously vanish after they're saved. A bit of digging later revealed it's because Dialogic (or Godot?) isn't adding the correct suffix when using this setting.

To Reproduce

1. Open Godot's editor settings. Under "Interface -> Editor", enable "Use Native File Dialogues".
2. Switch over to Dialogic and attempt to create a new timeline or style simply by typing its name (for instance, test_timeline).
3. See that the file isn't save properly, as Godot/Dialogic did not add the correct suffix.

Expected behavior
Dialogic should automatically add the suffix

System (please complete the following information):

• OS: Windows 10
• Godot Version: 4.4 Beta 1 / 4.3 (tested on both)
• Dialogic Version: 2.0 Alpha 16

Solutions

Workaround

Briefly disable the editor setting, or manually add the suffix to the end of files when using it.

Possible fixes

I don't know if it's a Godot issue or a scripting issue. I suspect it's an engine issue, as Godot does add the correct suffix without the Native File Dialogues option. I don't have enough technical knowledge to properly write a bug report in the main repo.