### 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
Color icon_pressed_color = accent_color * (dark_theme ? 1.15 : 3.5);
	icon_pressed_color.a = 1.0;
	const Color separator_color = Color(mono_color.r, mono_color.g, mono_color.b, 0.1);
	const Color highlight_color = Color(accent_color.r, accent_color.g, accent_color.b, 0.275);
	const Color disabled_highlight_color = highlight_color.lerp(dark_theme ? Color(0, 0, 0) : Color(1, 1, 1), 0.5);
	
	theme->set_color("icon_saturation", "Editor", Color(icon_saturation, icon_saturation, icon_saturation));
	theme->set_color("accent_color", "Editor", accent_color);
	theme->set_color("highlight_color", "Editor", highlight_color);
	theme->set_color("disabled_highlight_color", "Editor", disabled_highlight_color);
	theme->set_color("base_color", "Editor", base_color);
	theme->set_color("dark_color_1", "Editor", dark_color_1);
	theme->set_color("dark_color_2", "Editor", dark_color_2);
	theme->set_color("dark_color_3", "Editor", dark_color_3);
	theme->set_color("contrast_color_1", "Editor", contrast_color_1);
	theme->set_color("contrast_color_2", "Editor", contrast_color_2);
	theme->set_color("box_selection_fill_color", "Editor", accent_color * Color(1, 1, 1, 0.3));
	theme->set_color("box_selection_stroke_color", "Editor", accent_color * Color(1, 1, 1, 0.8));
	theme->set_color("axis_x_color", "Editor", Color(0.96, 0.20, 0.32));
	theme->set_color("axis_y_color", "Editor", Color(0.53, 0.84, 0.01));
	theme->set_color("axis_z_color", "Editor", Color(0.16, 0.55, 0.96));
	theme->set_color("axis_w_color", "Editor", Color(0.55, 0.55, 0.55));
	const float prop_color_saturation = accent_color.get_s() * 0.75;
	const float prop_color_value = accent_color.get_v();
	theme->set_color("property_color_x", "Editor", Color().from_hsv(0.0 / 3.0 + 0.05, prop_color_saturation, prop_color_value));
	theme->set_color("property_color_y", "Editor", Color().from_hsv(1.0 / 3.0 + 0.05, prop_color_saturation, prop_color_value));
	theme->set_color("property_color_z", "Editor", Color().from_hsv(2.0 / 3.0 + 0.05, prop_color_saturation, prop_color_value));
	theme->set_color("property_color_w", "Editor", Color().from_hsv(1.5 / 3.0 + 0.05, prop_color_saturation, prop_color_value));
	theme->set_color("font_color", "Editor", font_color);
	theme->set_color("highlighted_font_color", "Editor", font_hover_color);