### 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<StyleBoxTexture> style(memnew(StyleBoxTexture));
	style->set_texture(p_texture);
	style->set_texture_margin_individual(p_left * EDSCALE, p_top * EDSCALE, p_right * EDSCALE, p_bottom * EDSCALE);
	style->set_content_margin_individual((p_left + p_margin_left) * EDSCALE, (p_top + p_margin_top) * EDSCALE, (p_right + p_margin_right) * EDSCALE, (p_bottom + p_margin_bottom) * EDSCALE);
	style->set_draw_center(p_draw_center);
	return style;
}
static Ref<StyleBoxEmpty> make_empty_stylebox(float p_margin_left = -1, float p_margin_top = -1, float p_margin_right = -1, float p_margin_bottom = -1) {
	Ref<StyleBoxEmpty> style(memnew(StyleBoxEmpty));
	style->set_content_margin_individual(p_margin_left * EDSCALE, p_margin_top * EDSCALE, p_margin_right * EDSCALE, p_margin_bottom * EDSCALE);
	return style;
}
static Ref<StyleBoxFlat> make_flat_stylebox(Color p_color, float p_margin_left = -1, float p_margin_top = -1, float p_margin_right = -1, float p_margin_bottom = -1, int p_corner_width = 0) {
	Ref<StyleBoxFlat> style(memnew(StyleBoxFlat));
	style->set_bg_color(p_color);
	
	style->set_corner_detail(Math::ceil(0.8 * p_corner_width * EDSCALE));
	style->set_corner_radius_all(p_corner_width * EDSCALE);
	style->set_content_margin_individual(p_margin_left * EDSCALE, p_margin_top * EDSCALE, p_margin_right * EDSCALE, p_margin_bottom * EDSCALE);
	
	style->set_anti_aliased(false);
	return style;
}
static Ref<StyleBoxLine> make_line_stylebox(Color p_color, int p_thickness = 1, float p_grow_begin = 1, float p_grow_end = 1, bool p_vertical = false) {