### 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
Ref<StyleBoxFlat> style_widget_focus_viewport = style_widget_focus->duplicate();
	style_widget_focus_viewport->set_border_color(accent_color * Color(1, 1, 1, 0.5));
	theme->set_stylebox("FocusViewport", "EditorStyles", style_widget_focus_viewport);
	
	Ref<StyleBoxFlat> style_menu = style_widget->duplicate();
	style_menu->set_draw_center(false);
	style_menu->set_border_width_all(0);
	theme->set_stylebox("panel", "PanelContainer", style_menu);
	theme->set_stylebox("MenuPanel", "EditorStyles", style_menu);
	
	Ref<StyleBoxFlat> style_canvas_editor_info = make_flat_stylebox(Color(0.0, 0.0, 0.0, 0.2));
	style_canvas_editor_info->set_expand_margin_all(4 * EDSCALE);
	theme->set_stylebox("CanvasItemInfoOverlay", "EditorStyles", style_canvas_editor_info);
	
	
	
	
	Ref<StyleBoxFlat> toolbar_stylebox = memnew(StyleBoxFlat);
	toolbar_stylebox->set_bg_color(accent_color * Color(1, 1, 1, 0.1));
	toolbar_stylebox->set_corner_radius(CORNER_TOP_LEFT, corner_radius * EDSCALE);
	toolbar_stylebox->set_corner_radius(CORNER_TOP_RIGHT, corner_radius * EDSCALE);
	toolbar_stylebox->set_anti_aliased(false);
	
	toolbar_stylebox->set_border_color(accent_color);
	toolbar_stylebox->set_border_width(SIDE_BOTTOM, Math::round(2 * EDSCALE));
	toolbar_stylebox->set_content_margin(SIDE_BOTTOM, 0);
	theme->set_stylebox("ContextualToolbar", "EditorStyles", toolbar_stylebox);
	
	theme->set_stylebox("ScriptEditorPanel", "EditorStyles", make_empty_stylebox(default_margin_size, 0, default_margin_size, default_margin_size));
	theme->set_stylebox("ScriptEditorPanelFloating", "EditorStyles", make_empty_stylebox(0, 0, 0, 0));