### 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
style_window_title->set_corner_radius(CORNER_TOP_LEFT, 0);
	style_window_title->set_corner_radius(CORNER_TOP_RIGHT, 0);
	
	style_window_title->set_expand_margin(SIDE_BOTTOM, 2 * EDSCALE);
	Ref<StyleBoxFlat> style_window = style_popup->duplicate();
	style_window->set_border_color(base_color);
	style_window->set_border_width(SIDE_TOP, 24 * EDSCALE);
	style_window->set_expand_margin(SIDE_TOP, 24 * EDSCALE);
	theme->set_stylebox("embedded_border", "Window", style_window);
	theme->set_stylebox("embedded_unfocused_border", "Window", style_window);
	theme->set_color("title_color", "Window", font_color);
	theme->set_icon("close", "Window", theme->get_icon(SNAME("GuiClose"), SNAME("EditorIcons")));
	theme->set_icon("close_pressed", "Window", theme->get_icon(SNAME("GuiClose"), SNAME("EditorIcons")));
	theme->set_constant("close_h_offset", "Window", 22 * EDSCALE);
	theme->set_constant("close_v_offset", "Window", 20 * EDSCALE);
	theme->set_constant("title_height", "Window", 24 * EDSCALE);
	theme->set_constant("resize_margin", "Window", 4 * EDSCALE);
	theme->set_font("title_font", "Window", theme->get_font(SNAME("title"), SNAME("EditorFonts")));
	theme->set_font_size("title_font_size", "Window", theme->get_font_size(SNAME("title_size"), SNAME("EditorFonts")));
	
	Ref<StyleBoxFlat> style_complex_window = style_window->duplicate();
	style_complex_window->set_bg_color(dark_color_2);
	style_complex_window->set_border_color(dark_color_2);
	theme->set_stylebox("panel", "EditorSettingsDialog", style_complex_window);
	theme->set_stylebox("panel", "ProjectSettingsEditor", style_complex_window);
	theme->set_stylebox("panel", "EditorAbout", style_complex_window);
	
	theme->set_stylebox("panel", "AcceptDialog", style_window_title);
	theme->set_constant("buttons_separation", "AcceptDialog", 8 * EDSCALE);