### 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
if (snap_step.x != 0) {
			if (snap_separation.x == 0) {
				for (int i = 0; i < s.width; i++) {
					int cell = Math::fast_ftoi(Math::floor((mtx.affine_inverse().xform(Vector2(i, 0)).x - snap_offset.x) / snap_step.x));
					if (i == 0) {
						last_cell = cell;
					}
					if (last_cell != cell) {
						edit_draw->draw_line(Point2(i, 0), Point2(i, s.height), grid_color);
					}
					last_cell = cell;
				}
			} else {
				for (int i = 0; i < s.width; i++) {
					int cell = Math::fast_ftoi(Math::floor((mtx.affine_inverse().xform(Vector2(i, 0)).x - snap_offset.x) / (snap_step.x + snap_separation.x)));
					if (i == 0) {
						last_cell = cell;
					}
					if (last_cell != cell) {
						edit_draw->draw_rect(Rect2(i - snap_separation.x * draw_zoom, 0, snap_separation.x * draw_zoom, s.height), grid_color);
					}
					last_cell = cell;
				}
			}
		}
		if (snap_step.y != 0) {
			if (snap_separation.y == 0) {
				for (int i = 0; i < s.height; i++) {
					int cell = Math::fast_ftoi(Math::floor((mtx.affine_inverse().xform(Vector2(0, i)).y - snap_offset.y) / snap_step.y));
					if (i == 0) {