### 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
Ref<StyleBoxFlat> style_editor_help = style_default->duplicate();
	style_editor_help->set_bg_color(dark_color_2);
	style_editor_help->set_border_color(dark_color_3);
	theme->set_stylebox("background", "EditorHelp", style_editor_help);
	theme->set_color("title_color", "EditorHelp", accent_color);
	theme->set_color("headline_color", "EditorHelp", mono_color);
	theme->set_color("text_color", "EditorHelp", font_color);
	theme->set_color("comment_color", "EditorHelp", font_color * Color(1, 1, 1, 0.6));
	theme->set_color("symbol_color", "EditorHelp", font_color * Color(1, 1, 1, 0.6));
	theme->set_color("value_color", "EditorHelp", font_color * Color(1, 1, 1, 0.6));
	theme->set_color("qualifier_color", "EditorHelp", font_color * Color(1, 1, 1, 0.8));
	theme->set_color("type_color", "EditorHelp", accent_color.lerp(font_color, 0.5));
	theme->set_color("selection_color", "EditorHelp", selection_color);
	theme->set_color("link_color", "EditorHelp", accent_color.lerp(mono_color, 0.8));
	theme->set_color("code_color", "EditorHelp", accent_color.lerp(mono_color, 0.6));
	theme->set_color("kbd_color", "EditorHelp", accent_color.lerp(property_color, 0.6));
	theme->set_color("code_bg_color", "EditorHelp", dark_color_3);
	theme->set_color("kbd_bg_color", "EditorHelp", dark_color_1);
	theme->set_color("param_bg_color", "EditorHelp", dark_color_1);
	theme->set_constant("line_separation", "EditorHelp", Math::round(6 * EDSCALE));
	theme->set_constant("table_h_separation", "EditorHelp", 16 * EDSCALE);
	theme->set_constant("table_v_separation", "EditorHelp", 6 * EDSCALE);
	theme->set_constant("text_highlight_h_padding", "EditorHelp", 1 * EDSCALE);
	theme->set_constant("text_highlight_v_padding", "EditorHelp", 2 * EDSCALE);
	
	theme->set_stylebox("panel", "Panel", make_flat_stylebox(dark_color_1, 6, 4, 6, 4, corner_width));
	theme->set_stylebox("PanelForeground", "EditorStyles", style_default);
	
	theme->set_stylebox("normal", "Label", style_empty);
	theme->set_color("font_color", "Label", font_color);