Draw the UI debug overlay using the UI renderer (#16693)

# Objective

Draw the UI debug overlay using the UI renderer.

Significantly simpler and easier to use than
`bevy_dev_tools::ui_debug_overlay` which uses `bevy_gizmos`.
* Supports multiple windows and UI rendered to texture.
* Draws rounded debug rects for rounded UI nodes. 

Fixes #16666

## Solution

Removed the `ui_debug_overlay` module from `bevy_dev_tools`.

Added a `bevy_ui_debug` feature gate.

Draw the UI debug overlay using the UI renderer.
Adds a new module `bevy_ui::render::debug_overlay`. 

The debug overlay extraction function queries for the existing UI layout
and then adds a border around each UI node with `u32::MAX / 2` added to
each stack index so it's drawn on top.

There is a `UiDebugOptions` resource that can be used to enable or
disable the debug overlay and set the line width.

## Testing

The `testbed_ui` example has been changed to use the new debug overlay:

```
cargo run --example testbed_ui --features bevy_ui_debug
```

Press Space to toggle the debug overlay on and off.

---

## Showcase

<img width="961" alt="testbed-ui-new-debug"
src="https://github.com/user-attachments/assets/e9523d18-39ae-46a8-adbe-7d3f3ab8e951">

## Migration Guide

The `ui_debug_overlay` module has been removed from `bevy_dev_tools`.
There is a new debug overlay implemented using the `bevy_ui` renderer.
To use it, enable the `bevy_ui_debug` feature and set the `enable` field
of the `UiDebugOptions` resource to `true`.

Cargo.toml

@@ -156,6 +156,9 @@ bevy_ui_picking_backend = [
   "bevy_internal/bevy_ui_picking_backend",
 ]
 
+# Provides a debug overlay for bevy UI
+bevy_ui_debug = ["bevy_internal/bevy_ui_debug"]
+
 # Force dynamic linking, which improves iterative compile times
 dynamic_linking = ["dep:bevy_dylib", "bevy_internal/dynamic_linking"]
 

crates/bevy_dev_tools/Cargo.toml

@@ -9,29 +9,19 @@ license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]
-default = ["bevy_ui_debug"]
 bevy_ci_testing = ["serde", "ron"]
-bevy_ui_debug = []
 
 [dependencies]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.15.0-dev" }
 bevy_asset = { path = "../bevy_asset", version = "0.15.0-dev" }
 bevy_color = { path = "../bevy_color", version = "0.15.0-dev" }
-bevy_core = { path = "../bevy_core", version = "0.15.0-dev" }
-bevy_core_pipeline = { path = "../bevy_core_pipeline", version = "0.15.0-dev" }
 bevy_diagnostic = { path = "../bevy_diagnostic", version = "0.15.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev" }
-bevy_gizmos = { path = "../bevy_gizmos", version = "0.15.0-dev", features = [
-  "bevy_render",
-] }
 bevy_hierarchy = { path = "../bevy_hierarchy", version = "0.15.0-dev" }
 bevy_input = { path = "../bevy_input", version = "0.15.0-dev" }
-bevy_math = { path = "../bevy_math", version = "0.15.0-dev" }
-bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev" }
 bevy_render = { path = "../bevy_render", version = "0.15.0-dev" }
 bevy_time = { path = "../bevy_time", version = "0.15.0-dev" }
-bevy_transform = { path = "../bevy_transform", version = "0.15.0-dev" }
 bevy_text = { path = "../bevy_text", version = "0.15.0-dev" }
 bevy_ui = { path = "../bevy_ui", version = "0.15.0-dev" }
 bevy_utils = { path = "../bevy_utils", version = "0.15.0-dev" }

crates/bevy_dev_tools/src/lib.rs

@@ -15,9 +15,6 @@ pub mod ci_testing;
 
 pub mod fps_overlay;
 
-#[cfg(feature = "bevy_ui_debug")]
-pub mod ui_debug_overlay;
-
 pub mod states;
 
 /// Enables developer tools in an [`App`]. This plugin is added automatically with `bevy_dev_tools`