### 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> control_editor_popup_style = style_popup->duplicate();
	control_editor_popup_style->set_shadow_size(0);
	control_editor_popup_style->set_content_margin(SIDE_LEFT, default_margin_size * EDSCALE);
	control_editor_popup_style->set_content_margin(SIDE_TOP, default_margin_size * EDSCALE);
	control_editor_popup_style->set_content_margin(SIDE_RIGHT, default_margin_size * EDSCALE);
	control_editor_popup_style->set_content_margin(SIDE_BOTTOM, default_margin_size * EDSCALE);
	control_editor_popup_style->set_border_width_all(0);
	theme->set_stylebox("panel", "ControlEditorPopupPanel", control_editor_popup_style);
	theme->set_type_variation("ControlEditorPopupPanel", "PopupPanel");
	
	theme->set_icon("updown", "SpinBox", theme->get_icon(SNAME("GuiSpinboxUpdown"), SNAME("EditorIcons")));
	theme->set_icon("updown_disabled", "SpinBox", theme->get_icon(SNAME("GuiSpinboxUpdownDisabled"), SNAME("EditorIcons")));
	
	theme->set_stylebox("background", "ProgressBar", make_stylebox(theme->get_icon(SNAME("GuiProgressBar"), SNAME("EditorIcons")), 4, 4, 4, 4, 0, 0, 0, 0));
	theme->set_stylebox("fill", "ProgressBar", make_stylebox(theme->get_icon(SNAME("GuiProgressFill"), SNAME("EditorIcons")), 6, 6, 6, 6, 2, 1, 2, 1));
	theme->set_color("font_color", "ProgressBar", font_color);
	theme->set_color("font_outline_color", "ProgressBar", font_outline_color);
	theme->set_constant("outline_size", "ProgressBar", 0);
	
	theme->set_stylebox("panel", "GraphEdit", style_tree_bg);
	if (dark_theme) {
		theme->set_color("grid_major", "GraphEdit", Color(1.0, 1.0, 1.0, 0.15));
		theme->set_color("grid_minor", "GraphEdit", Color(1.0, 1.0, 1.0, 0.07));
	} else {
		theme->set_color("grid_major", "GraphEdit", Color(0.0, 0.0, 0.0, 0.15));
		theme->set_color("grid_minor", "GraphEdit", Color(0.0, 0.0, 0.0, 0.07));
	}
	theme->set_color("selection_fill", "GraphEdit", theme->get_color(SNAME("box_selection_fill_color"), SNAME("Editor")));
	theme->set_color("selection_stroke", "GraphEdit", theme->get_color(SNAME("box_selection_stroke_color"), SNAME("Editor")));
	theme->set_color("activity", "GraphEdit", accent_color);