### 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_icon("dismiss", "AssetLib", theme->get_icon(SNAME("Close"), SNAME("EditorIcons")));
	
	theme->set_color("preview_picker_overlay_color", "ThemeEditor", Color(0.1, 0.1, 0.1, 0.25));
	Color theme_preview_picker_bg_color = accent_color;
	theme_preview_picker_bg_color.a = 0.2;
	Ref<StyleBoxFlat> theme_preview_picker_sb = make_flat_stylebox(theme_preview_picker_bg_color, 0, 0, 0, 0);
	theme_preview_picker_sb->set_border_color(accent_color);
	theme_preview_picker_sb->set_border_width_all(1.0 * EDSCALE);
	theme->set_stylebox("preview_picker_overlay", "ThemeEditor", theme_preview_picker_sb);
	Color theme_preview_picker_label_bg_color = accent_color;
	theme_preview_picker_label_bg_color.set_v(0.5);
	Ref<StyleBoxFlat> theme_preview_picker_label_sb = make_flat_stylebox(theme_preview_picker_label_bg_color, 4.0, 1.0, 4.0, 3.0);
	theme->set_stylebox("preview_picker_label", "ThemeEditor", theme_preview_picker_label_sb);
	
	
	Ref<StyleBoxFlat> style_dictionary_add_item = make_flat_stylebox(prop_subsection_color, 0, 4, 0, 4, corner_radius);
	style_dictionary_add_item->set_expand_margin(SIDE_LEFT, 4 * EDSCALE);
	style_dictionary_add_item->set_expand_margin(SIDE_RIGHT, 4 * EDSCALE);
	theme->set_stylebox("DictionaryAddItem", "EditorStyles", style_dictionary_add_item);
	Ref<StyleBoxEmpty> vshader_label_style = make_empty_stylebox(2, 1, 2, 1);
	theme->set_stylebox("label_style", "VShaderEditor", vshader_label_style);
	
	theme->set_stylebox("search_panel", "ProjectManager", style_tree_bg);
	theme->set_constant("sidebar_button_icon_separation", "ProjectManager", int(6 * EDSCALE));
	
	
	const Color dim_color = Color(font_color.r, font_color.g, font_color.b, 0.5);
	const float mono_value = mono_color.r;
	const Color alpha1 = Color(mono_value, mono_value, mono_value, 0.07);
	const Color alpha2 = Color(mono_value, mono_value, mono_value, 0.14);