### 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("scroll_border", "Tree", 40 * EDSCALE);
	theme->set_constant("scroll_speed", "Tree", 12);
	theme->set_constant("outline_size", "Tree", 0);
	theme->set_constant("scrollbar_margin_left", "Tree", 0);
	theme->set_constant("scrollbar_margin_top", "Tree", 0);
	theme->set_constant("scrollbar_margin_right", "Tree", 0);
	theme->set_constant("scrollbar_margin_bottom", "Tree", 0);
	theme->set_constant("scrollbar_h_separation", "Tree", 1 * EDSCALE);
	theme->set_constant("scrollbar_v_separation", "Tree", 1 * EDSCALE);
	const Color guide_color = mono_color * Color(1, 1, 1, 0.05);
	Color relationship_line_color = mono_color * Color(1, 1, 1, relationship_line_opacity);
	theme->set_constant("draw_guides", "Tree", relationship_line_opacity < 0.01);
	theme->set_color("guide_color", "Tree", guide_color);
	int relationship_line_width = 1;
	Color parent_line_color = mono_color * Color(1, 1, 1, CLAMP(relationship_line_opacity + 0.45, 0.0, 1.0));
	Color children_line_color = mono_color * Color(1, 1, 1, CLAMP(relationship_line_opacity + 0.25, 0.0, 1.0));
	theme->set_constant("draw_relationship_lines", "Tree", relationship_line_opacity >= 0.01);
	theme->set_constant("relationship_line_width", "Tree", relationship_line_width);
	theme->set_constant("parent_hl_line_width", "Tree", relationship_line_width * 2);
	theme->set_constant("children_hl_line_width", "Tree", relationship_line_width);
	theme->set_constant("parent_hl_line_margin", "Tree", relationship_line_width * 3);
	theme->set_color("relationship_line_color", "Tree", relationship_line_color);
	theme->set_color("parent_hl_line_color", "Tree", parent_line_color);
	theme->set_color("children_hl_line_color", "Tree", children_line_color);
	Ref<StyleBoxFlat> style_tree_btn = style_default->duplicate();
	style_tree_btn->set_bg_color(highlight_color);
	style_tree_btn->set_border_width_all(0);
	theme->set_stylebox("button_pressed", "Tree", style_tree_btn);
	Ref<StyleBoxFlat> style_tree_hover = style_default->duplicate();
	style_tree_hover->set_bg_color(highlight_color * Color(1, 1, 1, 0.4));