Extract borders without border radius (#15020)

# Objective

The `BorderRadius` component shouldn't be required to draw borders for
nodes with sharp corners.

## Solution

Make `BorderRadius` optional in `extract_uinode_borders`'s UI node
query.

crates/bevy_ui/src/render/mod.rs

@@ -508,7 +508,7 @@ pub fn extract_uinode_borders(
  Option<&Parent>,
  &Style,
  &BorderColor,
- &BorderRadius,
+ Option<&BorderRadius>,
  ),
  Without<ContentSize>,
  >,
@@ -526,7 +526,7 @@ pub fn extract_uinode_borders(
  parent,
  style,
  border_color,
- border_radius,
+ maybe_border_radius,
  ) in &uinode_query
  {
  let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
@@ -574,14 +574,17 @@ pub fn extract_uinode_borders(
  continue;
  }
 
- let border_radius = resolve_border_radius(
- border_radius,
- node.size(),
- ui_logical_viewport_size,
- ui_scale.0,
- );
-
- let border_radius = clamp_radius(border_radius, node.size(), border.into());
+ let border_radius = if let Some(border_radius) = maybe_border_radius {
+ let resolved_radius = resolve_border_radius(
+ border_radius,
+ node.size(),
+ ui_logical_viewport_size,
+ ui_scale.0,
+ );
+ clamp_radius(resolved_radius, node.size(), border.into())
+ } else {
+ [0.; 4]
+ };
  let transform = global_transform.compute_matrix();
 
  extracted_uinodes.uinodes.insert(