### 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("decrement_highlight", "VScrollBar", empty_icon);
	theme->set_icon("decrement_pressed", "VScrollBar", empty_icon);
	
	theme->set_icon("grabber_highlight", "HSlider", theme->get_icon(SNAME("GuiSliderGrabberHl"), SNAME("EditorIcons")));
	theme->set_icon("grabber", "HSlider", theme->get_icon(SNAME("GuiSliderGrabber"), SNAME("EditorIcons")));
	theme->set_stylebox("slider", "HSlider", make_flat_stylebox(dark_color_3, 0, default_margin_size / 2, 0, default_margin_size / 2, corner_width));
	theme->set_stylebox("grabber_area", "HSlider", make_flat_stylebox(contrast_color_1, 0, default_margin_size / 2, 0, default_margin_size / 2, corner_width));
	theme->set_stylebox("grabber_area_highlight", "HSlider", make_flat_stylebox(contrast_color_1, 0, default_margin_size / 2, 0, default_margin_size / 2));
	theme->set_constant("center_grabber", "HSlider", 0);
	theme->set_constant("grabber_offset", "HSlider", 0);
	
	theme->set_icon("grabber", "VSlider", theme->get_icon(SNAME("GuiSliderGrabber"), SNAME("EditorIcons")));
	theme->set_icon("grabber_highlight", "VSlider", theme->get_icon(SNAME("GuiSliderGrabberHl"), SNAME("EditorIcons")));
	theme->set_stylebox("slider", "VSlider", make_flat_stylebox(dark_color_3, default_margin_size / 2, 0, default_margin_size / 2, 0, corner_width));
	theme->set_stylebox("grabber_area", "VSlider", make_flat_stylebox(contrast_color_1, default_margin_size / 2, 0, default_margin_size / 2, 0, corner_width));
	theme->set_stylebox("grabber_area_highlight", "VSlider", make_flat_stylebox(contrast_color_1, default_margin_size / 2, 0, default_margin_size / 2, 0));
	theme->set_constant("center_grabber", "VSlider", 0);
	theme->set_constant("grabber_offset", "VSlider", 0);
	
	theme->set_color("default_color", "RichTextLabel", font_color);
	theme->set_color("font_shadow_color", "RichTextLabel", Color(0, 0, 0, 0));
	theme->set_color("font_outline_color", "RichTextLabel", font_outline_color);
	theme->set_color("selection_color", "RichTextLabel", selection_color);
	theme->set_constant("shadow_offset_x", "RichTextLabel", 1 * EDSCALE);
	theme->set_constant("shadow_offset_y", "RichTextLabel", 1 * EDSCALE);
	theme->set_constant("shadow_outline_size", "RichTextLabel", 1 * EDSCALE);
	theme->set_constant("outline_size", "RichTextLabel", 0);
	theme->set_stylebox("focus", "RichTextLabel", make_empty_stylebox());
	theme->set_stylebox("normal", "RichTextLabel", style_tree_bg);