### 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_constant("sv_width", "ColorPicker", 256 * EDSCALE);
	theme->set_constant("sv_height", "ColorPicker", 256 * EDSCALE);
	theme->set_constant("h_width", "ColorPicker", 30 * EDSCALE);
	theme->set_constant("label_width", "ColorPicker", 10 * EDSCALE);
	theme->set_constant("center_slider_grabbers", "ColorPicker", 1);
	theme->set_icon("screen_picker", "ColorPicker", theme->get_icon(SNAME("ColorPick"), SNAME("EditorIcons")));
	theme->set_icon("shape_circle", "ColorPicker", theme->get_icon(SNAME("PickerShapeCircle"), SNAME("EditorIcons")));
	theme->set_icon("shape_rect", "ColorPicker", theme->get_icon(SNAME("PickerShapeRectangle"), SNAME("EditorIcons")));
	theme->set_icon("shape_rect_wheel", "ColorPicker", theme->get_icon(SNAME("PickerShapeRectangleWheel"), SNAME("EditorIcons")));
	theme->set_icon("add_preset", "ColorPicker", theme->get_icon(SNAME("Add"), SNAME("EditorIcons")));
	theme->set_icon("sample_bg", "ColorPicker", theme->get_icon(SNAME("GuiMiniCheckerboard"), SNAME("EditorIcons")));
	theme->set_icon("overbright_indicator", "ColorPicker", theme->get_icon(SNAME("OverbrightIndicator"), SNAME("EditorIcons")));
	theme->set_icon("bar_arrow", "ColorPicker", theme->get_icon(SNAME("ColorPickerBarArrow"), SNAME("EditorIcons")));
	theme->set_icon("picker_cursor", "ColorPicker", theme->get_icon(SNAME("PickerCursor"), SNAME("EditorIcons")));
	
	theme->set_icon("bg", "ColorPickerButton", theme->get_icon(SNAME("GuiMiniCheckerboard"), SNAME("EditorIcons")));
	
	Ref<StyleBoxFlat> preset_sb = make_flat_stylebox(Color(1, 1, 1), 2, 2, 2, 2, 2);
	theme->set_stylebox("preset_fg", "ColorPresetButton", preset_sb);
	theme->set_icon("preset_bg", "ColorPresetButton", theme->get_icon(SNAME("GuiMiniCheckerboard"), SNAME("EditorIcons")));
	theme->set_icon("overbright_indicator", "ColorPresetButton", theme->get_icon(SNAME("OverbrightIndicator"), SNAME("EditorIcons")));
	
	Ref<StyleBoxFlat> style_info_3d_viewport = style_default->duplicate();
	style_info_3d_viewport->set_bg_color(style_info_3d_viewport->get_bg_color() * Color(1, 1, 1, 0.5));
	style_info_3d_viewport->set_border_width_all(0);
	theme->set_stylebox("Information3dViewport", "EditorStyles", style_info_3d_viewport);
	
	theme->set_stylebox("bg", "AssetLib", style_empty);
	theme->set_stylebox("panel", "AssetLib", style_content_panel);
	theme->set_color("status_color", "AssetLib", Color(0.5, 0.5, 0.5));