### 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
obj_styleBox = Ref<StyleBoxTexture>(nullptr);
	atlas_tex = Ref<AtlasTexture>(nullptr);
	preview_tex = Ref<CanvasTexture>(memnew(CanvasTexture));
	
	snap_step = EditorSettings::get_singleton()->get_project_metadata("texture_region_editor", "snap_step", Vector2(8, 8));
	snap_separation = EditorSettings::get_singleton()->get_project_metadata("texture_region_editor", "snap_separation", Vector2());
	snap_mode = EditorSettings::get_singleton()->get_project_metadata("texture_region_editor", "snap_mode", SNAP_NONE);
	edited_margin = -1;
	drag_index = -1;
	drag = false;
	HBoxContainer *hb_tools = memnew(HBoxContainer);
	vb->add_child(hb_tools);
	hb_tools->add_child(memnew(Label(TTR("Snap Mode:"))));
	snap_mode_button = memnew(OptionButton);
	hb_tools->add_child(snap_mode_button);
	snap_mode_button->add_item(TTR("None"), 0);
	snap_mode_button->add_item(TTR("Pixel Snap"), 1);
	snap_mode_button->add_item(TTR("Grid Snap"), 2);
	snap_mode_button->add_item(TTR("Auto Slice"), 3);
	snap_mode_button->select(0);
	snap_mode_button->connect("item_selected", callable_mp(this, &TextureRegionEditor::_set_snap_mode));
	hb_grid = memnew(HBoxContainer);
	hb_tools->add_child(hb_grid);
	hb_grid->add_child(memnew(VSeparator));
	hb_grid->add_child(memnew(Label(TTR("Offset:"))));
	sb_off_x = memnew(SpinBox);
	sb_off_x->set_min(-256);
	sb_off_x->set_max(256);
	sb_off_x->set_step(1);
	sb_off_x->set_value(snap_offset.x);