### 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
if (!atlas.is_valid()) {
		return;
	}
	Rect2 rc = region;
	if (rc.size.width == 0) {
		rc.size.width = atlas->get_width();
	}
	if (rc.size.height == 0) {
		rc.size.height = atlas->get_height();
	}
	Vector2 scale = p_rect.size / (region.size + margin.size);
	Rect2 dr(p_rect.position + margin.position * scale, rc.size * scale);
	atlas->draw_rect_region(p_canvas_item, dr, rc, p_modulate, p_transpose, filter_clip);
}
void AtlasTexture::draw_rect_region(RID p_canvas_item, const Rect2 &p_rect, const Rect2 &p_src_rect, const Color &p_modulate, bool p_transpose, bool p_clip_uv) const {
	
	if (!atlas.is_valid()) {
		return;
	}
	Rect2 dr;
	Rect2 src_c;
	get_rect_region(p_rect, p_src_rect, dr, src_c);
	atlas->draw_rect_region(p_canvas_item, dr, src_c, p_modulate, p_transpose, filter_clip);
}
bool AtlasTexture::get_rect_region(const Rect2 &p_rect, const Rect2 &p_src_rect, Rect2 &r_rect, Rect2 &r_src_rect) const {