### Godot version

v4.1.1.stable.official [bd6af8e0e]

### System information

Godot v4.1.1.stable - Ubuntu 22.04.2 LTS 22.04 - Vulkan (Forward+) - integrated Intel(R) UHD Graphics 615 (AML-KBL) () - Intel(R) Core(TM) i3-10100Y CPU @ 1.30GHz (4 Threads)

### Issue description

Summary: When editing the subregion of a StyleBoxTexture, it shows me the entire spritesheet of the Atlas texture, instead of the selected portion of the atlas, making it difficult (and non-intuitive) to correctly select the subregion I need. 

What I expect: I understand that the sub-region may be used to emulate the behavior of a nine-patch. So I would expect to see there the subregion that i selected previously from the Atlas as the texture to be shown.

I have only tested this in a Panel Container

### Steps to reproduce

I found this problem when doing these steps:

- Add a PanelContainer node
- In the inspector select Theme Overrrides -> Style -> new StyleBoxTexture
- In the texture of the StyleBoxTexture select new AtlasTexture
- Dropped the spritesheet in the Atlas of the AtlasTexture
- In Region of the AtlasTexture, selected Edit Region and drew the rectangle on the texture i want:
![image](https://github.com/godotengine/godot/assets/1207326/2e9624b1-63bc-4267-8d7f-59e82df7896e)

- Back in the StyleBoxTexture options, in Sub-Region, clicked on Edit Region to select the nine-patch region i need
- Here is where the region editor shows me the entire spritesheet and not the sub-texture i selected from the atlas. The image below shows the axis correctly positioned for the nine-patch to work, but it is not intuitive because it has to be positioned without seeing the correct texture, making it difficult to finetune for some textures.

![image](https://github.com/godotengine/godot/assets/1207326/a5023afd-7e4b-47c8-adfc-03fda7f6301b)


### Minimal reproduction project

N/A
theme->set_color("font_placeholder_color", "LineEdit", font_placeholder_color);
	theme->set_color("font_outline_color", "LineEdit", font_outline_color);
	theme->set_color("caret_color", "LineEdit", font_color);
	theme->set_color("selection_color", "LineEdit", selection_color);
	theme->set_color("clear_button_color", "LineEdit", font_color);
	theme->set_color("clear_button_color_pressed", "LineEdit", accent_color);
	theme->set_constant("minimum_character_width", "LineEdit", 4);
	theme->set_constant("outline_size", "LineEdit", 0);
	theme->set_constant("caret_width", "LineEdit", 1);
	
	theme->set_stylebox("normal", "TextEdit", style_line_edit);
	theme->set_stylebox("focus", "TextEdit", style_widget_focus);
	theme->set_stylebox("read_only", "TextEdit", style_line_edit_disabled);
	theme->set_icon("tab", "TextEdit", theme->get_icon(SNAME("GuiTab"), SNAME("EditorIcons")));
	theme->set_icon("space", "TextEdit", theme->get_icon(SNAME("GuiSpace"), SNAME("EditorIcons")));
	theme->set_color("font_color", "TextEdit", font_color);
	theme->set_color("font_readonly_color", "TextEdit", font_readonly_color);
	theme->set_color("font_placeholder_color", "TextEdit", font_placeholder_color);
	theme->set_color("font_outline_color", "TextEdit", font_outline_color);
	theme->set_color("caret_color", "TextEdit", font_color);
	theme->set_color("selection_color", "TextEdit", selection_color);
	theme->set_color("background_color", "TextEdit", Color(0, 0, 0, 0));
	theme->set_constant("line_spacing", "TextEdit", 4 * EDSCALE);
	theme->set_constant("outline_size", "TextEdit", 0);
	theme->set_constant("caret_width", "TextEdit", 1);
	theme->set_icon("h_grabber", "SplitContainer", theme->get_icon(SNAME("GuiHsplitter"), SNAME("EditorIcons")));
	theme->set_icon("v_grabber", "SplitContainer", theme->get_icon(SNAME("GuiVsplitter"), SNAME("EditorIcons")));
	theme->set_icon("grabber", "VSplitContainer", theme->get_icon(SNAME("GuiVsplitter"), SNAME("EditorIcons")));
	theme->set_icon("grabber", "HSplitContainer", theme->get_icon(SNAME("GuiHsplitter"), SNAME("EditorIcons")));
	theme->set_constant("separation", "SplitContainer", default_margin_size * 2 * EDSCALE);