### 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
style_bottom_panel->set_corner_radius_all(corner_radius * EDSCALE);
	theme->set_stylebox("BottomPanel", "EditorStyles", style_bottom_panel);
	
	theme->set_type_variation("TabContainerOdd", "TabContainer");
	Ref<StyleBoxFlat> style_tab_selected_odd = style_tab_selected->duplicate();
	style_tab_selected_odd->set_bg_color(disabled_bg_color);
	theme->set_stylebox("tab_selected", "TabContainerOdd", style_tab_selected_odd);
	Ref<StyleBoxFlat> style_content_panel_odd = style_content_panel->duplicate();
	style_content_panel_odd->set_bg_color(disabled_bg_color);
	theme->set_stylebox("panel", "TabContainerOdd", style_content_panel_odd);
	
	Ref<StyleBoxFlat> style_content_panel_vp = style_content_panel->duplicate();
	style_content_panel_vp->set_content_margin_individual(border_width * 2, default_margin_size * EDSCALE, border_width * 2, border_width * 2);
	theme->set_stylebox("Content", "EditorStyles", style_content_panel_vp);
	
	Ref<StyleBoxFlat> style_theme_preview_tab = style_tab_selected_odd->duplicate();
	style_theme_preview_tab->set_expand_margin(SIDE_BOTTOM, 5 * EDSCALE);
	theme->set_stylebox("ThemeEditorPreviewFG", "EditorStyles", style_theme_preview_tab);
	Ref<StyleBoxFlat> style_theme_preview_bg_tab = style_tab_unselected->duplicate();
	style_theme_preview_bg_tab->set_expand_margin(SIDE_BOTTOM, 2 * EDSCALE);
	theme->set_stylebox("ThemeEditorPreviewBG", "EditorStyles", style_theme_preview_bg_tab);
	
	theme->set_stylebox("separator", "HSeparator", make_line_stylebox(separator_color, MAX(Math::round(EDSCALE), border_width)));
	theme->set_stylebox("separator", "VSeparator", make_line_stylebox(separator_color, MAX(Math::round(EDSCALE), border_width), 0, 0, true));
	
	Ref<StyleBoxFlat> style_panel_debugger = style_content_panel->duplicate();
	style_panel_debugger->set_border_width(SIDE_BOTTOM, 0);
	theme->set_stylebox("DebuggerPanel", "EditorStyles", style_panel_debugger);
	Ref<StyleBoxFlat> style_panel_invisible_top = style_content_panel->duplicate();
	int stylebox_offset = theme->get_font(SNAME("tab_selected"), SNAME("TabContainer"))->get_height(theme->get_font_size(SNAME("tab_selected"), SNAME("TabContainer"))) + theme->get_stylebox(SNAME("tab_selected"), SNAME("TabContainer"))->get_minimum_size().height + theme->get_stylebox(SNAME("panel"), SNAME("TabContainer"))->get_content_margin(SIDE_TOP);