### 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_color("disabled_font_color", "Editor", font_disabled_color);
	theme->set_color("readonly_font_color", "Editor", font_readonly_color);
	theme->set_color("mono_color", "Editor", mono_color);
	Color success_color = Color(0.45, 0.95, 0.5);
	Color warning_color = Color(1, 0.87, 0.4);
	Color error_color = Color(1, 0.47, 0.42);
	Color property_color = font_color.lerp(Color(0.5, 0.5, 0.5), 0.5);
	Color readonly_color = property_color.lerp(dark_theme ? Color(0, 0, 0) : Color(1, 1, 1), 0.25);
	Color readonly_warning_color = error_color.lerp(dark_theme ? Color(0, 0, 0) : Color(1, 1, 1), 0.25);
	if (!dark_theme) {
		
		success_color = success_color.lerp(mono_color, 0.35);
		warning_color = warning_color.lerp(mono_color, 0.35);
		error_color = error_color.lerp(mono_color, 0.25);
	}
	theme->set_color("success_color", "Editor", success_color);
	theme->set_color("warning_color", "Editor", warning_color);
	theme->set_color("error_color", "Editor", error_color);
	theme->set_color("property_color", "Editor", property_color);
	theme->set_color("readonly_color", "Editor", readonly_color);
	if (!dark_theme) {
		theme->set_color("highend_color", "Editor", Color::hex(0xad1128ff));
	} else {
		theme->set_color("highend_color", "Editor", Color(1.0, 0.0, 0.0));
	}
	const int thumb_size = EDITOR_GET("filesystem/file_dialog/thumbnail_size");
	theme->set_constant("scale", "Editor", EDSCALE);
	theme->set_constant("thumb_size", "Editor", thumb_size);
	theme->set_constant("class_icon_size", "Editor", 16 * EDSCALE);
	theme->set_constant("dark_theme", "Editor", dark_theme);