### 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<Texture2D> empty_icon = memnew(ImageTexture);
	if (increase_scrollbar_touch_area) {
		theme->set_stylebox("scroll", "HScrollBar", make_line_stylebox(separator_color, 50));
	} else {
		theme->set_stylebox("scroll", "HScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollBg"), SNAME("EditorIcons")), 5, 5, 5, 5, 1, 1, 1, 1));
	}
	theme->set_stylebox("scroll_focus", "HScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollBg"), SNAME("EditorIcons")), 5, 5, 5, 5, 1, 1, 1, 1));
	theme->set_stylebox("grabber", "HScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollGrabber"), SNAME("EditorIcons")), 6, 6, 6, 6, 1, 1, 1, 1));
	theme->set_stylebox("grabber_highlight", "HScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollGrabberHl"), SNAME("EditorIcons")), 5, 5, 5, 5, 1, 1, 1, 1));
	theme->set_stylebox("grabber_pressed", "HScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollGrabberPressed"), SNAME("EditorIcons")), 6, 6, 6, 6, 1, 1, 1, 1));
	theme->set_icon("increment", "HScrollBar", empty_icon);
	theme->set_icon("increment_highlight", "HScrollBar", empty_icon);
	theme->set_icon("increment_pressed", "HScrollBar", empty_icon);
	theme->set_icon("decrement", "HScrollBar", empty_icon);
	theme->set_icon("decrement_highlight", "HScrollBar", empty_icon);
	theme->set_icon("decrement_pressed", "HScrollBar", empty_icon);
	
	if (increase_scrollbar_touch_area) {
		theme->set_stylebox("scroll", "VScrollBar", make_line_stylebox(separator_color, 50, 1, 1, true));
	} else {
		theme->set_stylebox("scroll", "VScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollBg"), SNAME("EditorIcons")), 5, 5, 5, 5, 1, 1, 1, 1));
	}
	theme->set_stylebox("scroll_focus", "VScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollBg"), SNAME("EditorIcons")), 5, 5, 5, 5, 1, 1, 1, 1));
	theme->set_stylebox("grabber", "VScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollGrabber"), SNAME("EditorIcons")), 6, 6, 6, 6, 1, 1, 1, 1));
	theme->set_stylebox("grabber_highlight", "VScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollGrabberHl"), SNAME("EditorIcons")), 5, 5, 5, 5, 1, 1, 1, 1));
	theme->set_stylebox("grabber_pressed", "VScrollBar", make_stylebox(theme->get_icon(SNAME("GuiScrollGrabberPressed"), SNAME("EditorIcons")), 6, 6, 6, 6, 1, 1, 1, 1));
	theme->set_icon("increment", "VScrollBar", empty_icon);
	theme->set_icon("increment_highlight", "VScrollBar", empty_icon);
	theme->set_icon("increment_pressed", "VScrollBar", empty_icon);
	theme->set_icon("decrement", "VScrollBar", empty_icon);