### 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
OS::get_singleton()->benchmark_begin_measure("create_editor_theme");
	Ref<Theme> theme = Ref<Theme>(memnew(Theme));
	
	theme->set_default_base_scale(EDSCALE);
	
	Color accent_color = EDITOR_GET("interface/theme/accent_color");
	Color base_color = EDITOR_GET("interface/theme/base_color");
	float contrast = EDITOR_GET("interface/theme/contrast");
	bool increase_scrollbar_touch_area = EDITOR_GET("interface/touchscreen/increase_scrollbar_touch_area");
	const float gizmo_handle_scale = EDITOR_GET("interface/touchscreen/scale_gizmo_handles");
	bool draw_extra_borders = EDITOR_GET("interface/theme/draw_extra_borders");
	float icon_saturation = EDITOR_GET("interface/theme/icon_saturation");
	float relationship_line_opacity = EDITOR_GET("interface/theme/relationship_line_opacity");
	String preset = EDITOR_GET("interface/theme/preset");
	int border_size = EDITOR_GET("interface/theme/border_size");
	int corner_radius = EDITOR_GET("interface/theme/corner_radius");
	Color preset_accent_color;
	Color preset_base_color;
	float preset_contrast = 0;
	bool preset_draw_extra_borders = false;
	const float default_contrast = 0.3;
	
	
	if (preset == "Custom") {
		accent_color = EDITOR_GET("interface/theme/accent_color");
		base_color = EDITOR_GET("interface/theme/base_color");
		contrast = EDITOR_GET("interface/theme/contrast");
	} else if (preset == "Breeze Dark") {
		preset_accent_color = Color(0.26, 0.76, 1.00);