### 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("color_picker_button_height", "Editor", 28 * EDSCALE);
	theme->set_constant("gizmo_handle_scale", "Editor", gizmo_handle_scale);
	theme->set_constant("window_border_margin", "Editor", 8);
	theme->set_constant("top_bar_separation", "Editor", 8 * EDSCALE);
	
	
	
	bool keep_old_icons = false;
	bool regenerate_thumb_icons = true;
	if (p_theme != nullptr) {
		
		
		
		const float prev_scale = (float)p_theme->get_constant(SNAME("scale"), SNAME("Editor"));
		const bool prev_dark_theme = (bool)p_theme->get_constant(SNAME("dark_theme"), SNAME("Editor"));
		const Color prev_accent_color = p_theme->get_color(SNAME("accent_color"), SNAME("Editor"));
		const float prev_icon_saturation = p_theme->get_color(SNAME("icon_saturation"), SNAME("Editor")).r;
		const float prev_gizmo_handle_scale = (float)p_theme->get_constant(SNAME("gizmo_handle_scale"), SNAME("Editor"));
		keep_old_icons = (Math::is_equal_approx(prev_scale, EDSCALE) &&
				Math::is_equal_approx(prev_gizmo_handle_scale, gizmo_handle_scale) &&
				prev_dark_theme == dark_theme &&
				prev_accent_color == accent_color &&
				prev_icon_saturation == icon_saturation);
		const double prev_thumb_size = (double)p_theme->get_constant(SNAME("thumb_size"), SNAME("Editor"));
		regenerate_thumb_icons = !Math::is_equal_approx(prev_thumb_size, thumb_size);
	}
#ifndef MODULE_SVG_ENABLED
	WARN_PRINT("SVG support disabled, editor icons won't be rendered.");
#endif
	if (keep_old_icons) {