Fix bevy_ui compile error when bevy_picking feature is disabled (#15053)

# Objective

#14957 added the `pick_rounded_rect` function to `bevy_ui` in the
`picking_backend` module, which is gated behind the `bevy_picking`
feature. This function is used in that module, as well as in the `focus`
module. The latter usage is not gated behind the `bevy_picking` feature,
causing a compile error when the feature is disabled.

## Solution

Move the `pick_rounded_rect` function out of the `picking_backend`
module, as it does not depend on anything defined in that module. I put
it in `lib.rs` but it could reasonably be moved somewhere else instead.

## Testing

Encountered this compile error in a project and confirmed that this
patch fixes it.

crates/bevy_ui/src/focus.rs

@@ -1,6 +1,5 @@
 use crate::{
-    picking_backend::pick_rounded_rect, CalculatedClip, DefaultUiCamera, Node, TargetCamera,
+    CalculatedClip, DefaultUiCamera, Node, ResolvedBorderRadius, TargetCamera, UiScale, UiStack,
-    UiScale, UiStack,
 };
 use bevy_ecs::{
     change_detection::DetectChangesMut,
@@ -343,3 +342,26 @@ pub fn ui_focus_system(
         }
     }
 }
+
+// Returns true if `point` (relative to the rectangle's center) is within the bounds of a rounded rectangle with
+// the given size and border radius.
+//
+// Matches the sdf function in `ui.wgsl` that is used by the UI renderer to draw rounded rectangles.
+pub(crate) fn pick_rounded_rect(
+    point: Vec2,
+    size: Vec2,
+    border_radius: ResolvedBorderRadius,
+) -> bool {
+    let s = point.signum();
+    let r = (border_radius.top_left * (1. - s.x) * (1. - s.y)
+        + border_radius.top_right * (1. + s.x) * (1. - s.y)
+        + border_radius.bottom_right * (1. + s.x) * (1. + s.y)
+        + border_radius.bottom_left * (1. - s.x) * (1. + s.y))
+        / 4.;
+
+    let corner_to_point = point.abs() - 0.5 * size;
+    let q = corner_to_point + r;
+    let l = q.max(Vec2::ZERO).length();
+    let m = q.max_element().min(0.);
+    l + m - r < 0.
+}

crates/bevy_ui/src/picking_backend.rs

@@ -23,7 +23,7 @@
 #![allow(clippy::too_many_arguments)]
 #![deny(missing_docs)]
 
-use crate::{prelude::*, UiStack};
+use crate::{focus::pick_rounded_rect, prelude::*, UiStack};
 use bevy_app::prelude::*;
 use bevy_ecs::{prelude::*, query::QueryData};
 use bevy_math::Vec2;
@@ -217,26 +217,3 @@ pub fn ui_picking(
         output.send(PointerHits::new(*pointer, picks, order));
     }
 }
-
-// Returns true if `point` (relative to the rectangle's center) is within the bounds of a rounded rectangle with
-// the given size and border radius.
-//
-// Matches the sdf function in `ui.wgsl` that is used by the UI renderer to draw rounded rectangles.
-pub(crate) fn pick_rounded_rect(
-    point: Vec2,
-    size: Vec2,
-    border_radius: ResolvedBorderRadius,
-) -> bool {
-    let s = point.signum();
-    let r = (border_radius.top_left * (1. - s.x) * (1. - s.y)
-        + border_radius.top_right * (1. + s.x) * (1. - s.y)
-        + border_radius.bottom_right * (1. + s.x) * (1. + s.y)
-        + border_radius.bottom_left * (1. - s.x) * (1. + s.y))
-        / 4.;
-
-    let corner_to_point = point.abs() - 0.5 * size;
-    let q = corner_to_point + r;
-    let l = q.max(Vec2::ZERO).length();
-    let m = q.max_element().min(0.);
-    l + m - r < 0.
-}