### 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_icon("can_fold", "CodeEdit", theme->get_icon(SNAME("CodeFoldDownArrow"), SNAME("EditorIcons")));
	theme->set_icon("executing_line", "CodeEdit", theme->get_icon(SNAME("TextEditorPlay"), SNAME("EditorIcons")));
	theme->set_icon("breakpoint", "CodeEdit", theme->get_icon(SNAME("Breakpoint"), SNAME("EditorIcons")));
	theme->set_constant("line_spacing", "CodeEdit", EDITOR_GET("text_editor/appearance/whitespace/line_spacing"));
	theme->set_color("background_color", "CodeEdit", Color(0, 0, 0, 0));
	theme->set_color("completion_background_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/completion_background_color"));
	theme->set_color("completion_selected_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/completion_selected_color"));
	theme->set_color("completion_existing_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/completion_existing_color"));
	theme->set_color("completion_scroll_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/completion_scroll_color"));
	theme->set_color("completion_scroll_hovered_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/completion_scroll_hovered_color"));
	theme->set_color("completion_font_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/completion_font_color"));
	theme->set_color("font_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/text_color"));
	theme->set_color("line_number_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/line_number_color"));
	theme->set_color("caret_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/caret_color"));
	theme->set_color("font_selected_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/text_selected_color"));
	theme->set_color("selection_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/selection_color"));
	theme->set_color("brace_mismatch_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/brace_mismatch_color"));
	theme->set_color("current_line_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/current_line_color"));
	theme->set_color("line_length_guideline_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/line_length_guideline_color"));
	theme->set_color("word_highlighted_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/word_highlighted_color"));
	theme->set_color("bookmark_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/bookmark_color"));
	theme->set_color("breakpoint_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/breakpoint_color"));
	theme->set_color("executing_line_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/executing_line_color"));
	theme->set_color("code_folding_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/code_folding_color"));
	theme->set_color("search_result_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/search_result_color"));
	theme->set_color("search_result_border_color", "CodeEdit", EDITOR_GET("text_editor/theme/highlighting/search_result_border_color"));
	OS::get_singleton()->benchmark_end_measure("create_editor_theme");
	return theme;
}
Ref<Theme> create_custom_theme(const Ref<Theme> p_theme) {