### 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_color("drop_mark_color", "TabBar", tab_highlight);
	theme->set_icon("menu", "TabContainer", theme->get_icon(SNAME("GuiTabMenu"), SNAME("EditorIcons")));
	theme->set_icon("menu_highlight", "TabContainer", theme->get_icon(SNAME("GuiTabMenuHl"), SNAME("EditorIcons")));
	theme->set_icon("close", "TabBar", theme->get_icon(SNAME("GuiClose"), SNAME("EditorIcons")));
	theme->set_icon("increment", "TabContainer", theme->get_icon(SNAME("GuiScrollArrowRight"), SNAME("EditorIcons")));
	theme->set_icon("decrement", "TabContainer", theme->get_icon(SNAME("GuiScrollArrowLeft"), SNAME("EditorIcons")));
	theme->set_icon("increment", "TabBar", theme->get_icon(SNAME("GuiScrollArrowRight"), SNAME("EditorIcons")));
	theme->set_icon("decrement", "TabBar", theme->get_icon(SNAME("GuiScrollArrowLeft"), SNAME("EditorIcons")));
	theme->set_icon("increment_highlight", "TabBar", theme->get_icon(SNAME("GuiScrollArrowRightHl"), SNAME("EditorIcons")));
	theme->set_icon("decrement_highlight", "TabBar", theme->get_icon(SNAME("GuiScrollArrowLeftHl"), SNAME("EditorIcons")));
	theme->set_icon("increment_highlight", "TabContainer", theme->get_icon(SNAME("GuiScrollArrowRightHl"), SNAME("EditorIcons")));
	theme->set_icon("decrement_highlight", "TabContainer", theme->get_icon(SNAME("GuiScrollArrowLeftHl"), SNAME("EditorIcons")));
	theme->set_icon("drop_mark", "TabContainer", theme->get_icon(SNAME("GuiTabDropMark"), SNAME("EditorIcons")));
	theme->set_icon("drop_mark", "TabBar", theme->get_icon(SNAME("GuiTabDropMark"), SNAME("EditorIcons")));
	theme->set_constant("side_margin", "TabContainer", 0);
	theme->set_constant("outline_size", "TabContainer", 0);
	theme->set_constant("h_separation", "TabBar", 4 * EDSCALE);
	theme->set_constant("outline_size", "TabBar", 0);
	
	Ref<StyleBoxFlat> style_content_panel = style_default->duplicate();
	style_content_panel->set_border_color(dark_color_3);
	style_content_panel->set_border_width_all(border_width);
	style_content_panel->set_border_width(Side::SIDE_TOP, 0);
	style_content_panel->set_corner_radius(CORNER_TOP_LEFT, 0);
	style_content_panel->set_corner_radius(CORNER_TOP_RIGHT, 0);
	
	style_content_panel->set_content_margin_individual(margin_size_extra * EDSCALE, (2 + margin_size_extra) * EDSCALE, margin_size_extra * EDSCALE, margin_size_extra * EDSCALE);
	theme->set_stylebox("panel", "TabContainer", style_content_panel);
	
	Ref<StyleBoxFlat> style_bottom_panel = style_content_panel->duplicate();