Simplify ui_picking's camera search (#22075)

# Objective

In `ui_picking` the camera_query iterator is run through multiple
filters and maps, which could be replaced by a single filter. Also
camera_query retrieves the `Camera` component but then it is thrown away
and queried for again.

## Solution

* Just collapse all the maps and filters into one `filter`.
* Only query for `Camera` once and keep the result, remove the second
query.

Author: ickshonpe

crates/bevy_ui/src/picking_backend.rs

@@ -119,33 +119,24 @@ pub fn ui_picking(
     {
         // This pointer is associated with a render target, which could be used by multiple
         // cameras. We want to ensure we return all cameras with a matching target.
-        for camera in camera_query
-            .iter()
-            .filter(|(_, _, cam_can_pick)| !settings.require_markers || *cam_can_pick)
-            .map(|(entity, camera, _)| {
-                (
-                    entity,
-                    camera.target.normalize(primary_window.single().ok()),
-                )
-            })
-            .filter_map(|(entity, target)| Some(entity).zip(target))
-            .filter(|(_entity, target)| target == &pointer_location.target)
-            .map(|(cam_entity, _target)| cam_entity)
-        {
-            let Ok((_, camera_data, _)) = camera_query.get(camera) else {
-                continue;
-            };
+        for (entity, camera, _) in camera_query.iter().filter(|(_, camera, cam_can_pick)| {
+            (!settings.require_markers || *cam_can_pick)
+                && camera
+                    .target
+                    .normalize(primary_window.single().ok())
+                    .is_some_and(|target| target == pointer_location.target)
+        }) {
             let mut pointer_pos =
-                pointer_location.position * camera_data.target_scaling_factor().unwrap_or(1.);
-            if let Some(viewport) = camera_data.physical_viewport_rect() {
+                pointer_location.position * camera.target_scaling_factor().unwrap_or(1.);
+            if let Some(viewport) = camera.physical_viewport_rect() {
                 if !viewport.as_rect().contains(pointer_pos) {
                     // The pointer is outside the viewport, skip it
                     continue;
                 }
                 pointer_pos -= viewport.min.as_vec2();
             }
             pointer_pos_by_camera
-                .entry(camera)
+                .entry(entity)
                 .or_default()
                 .insert(pointer_id, pointer_pos);
         }