### 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
sb_off_x->set_suffix("px");
	sb_off_x->connect("value_changed", callable_mp(this, &TextureRegionEditor::_set_snap_off_x));
	hb_grid->add_child(sb_off_x);
	sb_off_y = memnew(SpinBox);
	sb_off_y->set_min(-256);
	sb_off_y->set_max(256);
	sb_off_y->set_step(1);
	sb_off_y->set_value(snap_offset.y);
	sb_off_y->set_suffix("px");
	sb_off_y->connect("value_changed", callable_mp(this, &TextureRegionEditor::_set_snap_off_y));
	hb_grid->add_child(sb_off_y);
	hb_grid->add_child(memnew(VSeparator));
	hb_grid->add_child(memnew(Label(TTR("Step:"))));
	sb_step_x = memnew(SpinBox);
	sb_step_x->set_min(-256);
	sb_step_x->set_max(256);
	sb_step_x->set_step(1);
	sb_step_x->set_value(snap_step.x);
	sb_step_x->set_suffix("px");
	sb_step_x->connect("value_changed", callable_mp(this, &TextureRegionEditor::_set_snap_step_x));
	hb_grid->add_child(sb_step_x);
	sb_step_y = memnew(SpinBox);
	sb_step_y->set_min(-256);
	sb_step_y->set_max(256);
	sb_step_y->set_step(1);
	sb_step_y->set_value(snap_step.y);
	sb_step_y->set_suffix("px");
	sb_step_y->connect("value_changed", callable_mp(this, &TextureRegionEditor::_set_snap_step_y));
	hb_grid->add_child(sb_step_y);
	hb_grid->add_child(memnew(VSeparator));