### 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
for (int i = 0; i < editor_icons_count; i++) {
			theme->set_icon(editor_icons_names[i], SNAME("EditorIcons"), p_theme->get_icon(editor_icons_names[i], SNAME("EditorIcons")));
		}
	} else {
		editor_register_and_generate_icons(theme, dark_theme, icon_saturation, thumb_size, false);
	}
	if (regenerate_thumb_icons) {
		editor_register_and_generate_icons(theme, dark_theme, icon_saturation, thumb_size, true);
	}
	
	editor_register_fonts(theme);
	
	const int border_width = CLAMP(border_size, 0, 2) * MAX(1, EDSCALE);
	const int corner_width = CLAMP(corner_radius, 0, 6);
	const int default_margin_size = 4;
	const int margin_size_extra = default_margin_size + CLAMP(border_size, 0, 2);
	
	
	Ref<StyleBoxFlat> style_default = make_flat_stylebox(base_color, default_margin_size, default_margin_size, default_margin_size, default_margin_size, corner_width);
	style_default->set_border_width_all(border_width);
	style_default->set_border_color(base_color);
	
	const float extra_spacing = EDITOR_GET("interface/theme/additional_spacing");
	const Vector2 widget_default_margin = Vector2(extra_spacing + 6, extra_spacing + default_margin_size + 1) * EDSCALE;
	Ref<StyleBoxFlat> style_widget = style_default->duplicate();
	style_widget->set_content_margin_individual(widget_default_margin.x, widget_default_margin.y, widget_default_margin.x, widget_default_margin.y);
	style_widget->set_bg_color(dark_color_1);
	if (draw_extra_borders) {
		style_widget->set_border_width_all(Math::round(EDSCALE));
		style_widget->set_border_color(extra_border_color_1);