### 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
const Color dark_color_1 = base_color.lerp(Color(0, 0, 0, 1), contrast).clamp();
	const Color dark_color_2 = base_color.lerp(Color(0, 0, 0, 1), contrast * 1.5).clamp();
	const Color dark_color_3 = base_color.lerp(Color(0, 0, 0, 1), contrast * 2).clamp();
	
	const Color extra_border_color_1 = Color(0.5, 0.5, 0.5);
	const Color extra_border_color_2 = dark_theme ? Color(0.3, 0.3, 0.3) : Color(0.7, 0.7, 0.7);
	const Color background_color = dark_color_2;
	
	const Color mono_color = dark_theme ? Color(1, 1, 1) : Color(0, 0, 0);
	const Color contrast_color_1 = base_color.lerp(mono_color, MAX(contrast, default_contrast));
	const Color contrast_color_2 = base_color.lerp(mono_color, MAX(contrast * 1.5, default_contrast * 1.5));
	const Color font_color = mono_color.lerp(base_color, 0.25);
	const Color font_hover_color = mono_color.lerp(base_color, 0.125);
	const Color font_focus_color = mono_color.lerp(base_color, 0.125);
	const Color font_hover_pressed_color = font_hover_color.lerp(accent_color, 0.74);
	const Color font_disabled_color = Color(mono_color.r, mono_color.g, mono_color.b, 0.35);
	const Color font_readonly_color = Color(mono_color.r, mono_color.g, mono_color.b, 0.65);
	const Color font_placeholder_color = Color(mono_color.r, mono_color.g, mono_color.b, 0.6);
	const Color font_outline_color = Color(0, 0, 0, 0);
	const Color selection_color = accent_color * Color(1, 1, 1, 0.4);
	const Color disabled_color = mono_color.inverted().lerp(base_color, 0.7);
	const Color disabled_bg_color = mono_color.inverted().lerp(base_color, 0.9);
	const Color icon_normal_color = Color(1, 1, 1);
	Color icon_hover_color = icon_normal_color * (dark_theme ? 1.15 : 1.45);
	icon_hover_color.a = 1.0;
	Color icon_focus_color = icon_hover_color;
	Color icon_disabled_color = Color(icon_normal_color, 0.4);