### 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_stylebox("panel", "Tree", style_tree_bg);
	theme->set_stylebox("panel", "EditorValidationPanel", style_tree_bg);
	
	theme->set_icon("checked", "Tree", theme->get_icon(SNAME("GuiChecked"), SNAME("EditorIcons")));
	theme->set_icon("indeterminate", "Tree", theme->get_icon(SNAME("GuiIndeterminate"), SNAME("EditorIcons")));
	theme->set_icon("unchecked", "Tree", theme->get_icon(SNAME("GuiUnchecked"), SNAME("EditorIcons")));
	theme->set_icon("arrow", "Tree", theme->get_icon(SNAME("GuiTreeArrowDown"), SNAME("EditorIcons")));
	theme->set_icon("arrow_collapsed", "Tree", theme->get_icon(SNAME("GuiTreeArrowRight"), SNAME("EditorIcons")));
	theme->set_icon("arrow_collapsed_mirrored", "Tree", theme->get_icon(SNAME("GuiTreeArrowLeft"), SNAME("EditorIcons")));
	theme->set_icon("updown", "Tree", theme->get_icon(SNAME("GuiTreeUpdown"), SNAME("EditorIcons")));
	theme->set_icon("select_arrow", "Tree", theme->get_icon(SNAME("GuiDropdown"), SNAME("EditorIcons")));
	theme->set_stylebox("focus", "Tree", style_widget_focus);
	theme->set_stylebox("custom_button", "Tree", make_empty_stylebox());
	theme->set_stylebox("custom_button_pressed", "Tree", make_empty_stylebox());
	theme->set_stylebox("custom_button_hover", "Tree", style_widget);
	theme->set_color("custom_button_font_highlight", "Tree", font_hover_color);
	theme->set_color("font_color", "Tree", font_color);
	theme->set_color("font_selected_color", "Tree", mono_color);
	theme->set_color("font_outline_color", "Tree", font_outline_color);
	theme->set_color("title_button_color", "Tree", font_color);
	theme->set_color("drop_position_color", "Tree", accent_color);
	theme->set_constant("v_separation", "Tree", widget_default_margin.y - EDSCALE);
	theme->set_constant("h_separation", "Tree", 6 * EDSCALE);
	theme->set_constant("guide_width", "Tree", border_width);
	theme->set_constant("item_margin", "Tree", 3 * default_margin_size * EDSCALE);
	theme->set_constant("inner_item_margin_bottom", "Tree", (default_margin_size + extra_spacing) * EDSCALE);
	theme->set_constant("inner_item_margin_left", "Tree", (default_margin_size + extra_spacing) * EDSCALE);
	theme->set_constant("inner_item_margin_right", "Tree", (default_margin_size + extra_spacing) * EDSCALE);
	theme->set_constant("inner_item_margin_top", "Tree", (default_margin_size + extra_spacing) * EDSCALE);
	theme->set_constant("button_margin", "Tree", default_margin_size * EDSCALE);