bugfix(frustra of point lights were not recalculated when a camera changes)

[HugoPeters1024]

Objective

• Fixes Shadow is missing when initial camera pos is far away from the object #11682

Solution

• [Merged by Bors] - perf: only recalculate frusta of changed lights #4086 introduced an optimization to not do redundant calculations, but did not take into account changes to the resource global_lights. I believe that my patch includes the optimization benefit but adds the required nuance to fix said bug.

Testing

The example originally given by @kirillsurkov and then updated by me to bevy 15.3 here: #11682 (comment) will not have shadows without this patch:

use bevy::prelude::*;

#[derive(Resource)]
struct State {
    x: f32,
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, update)
        .insert_resource(State { x: -40.0 })
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn((
        Mesh3d(meshes.add(Circle::new(4.0))),
        MeshMaterial3d(materials.add(Color::WHITE)),
    ));
    commands.spawn((
        Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
        MeshMaterial3d(materials.add(Color::linear_rgb(0.0, 1.0, 0.0))),
    ));
    commands.spawn((
        PointLight {
            shadows_enabled: true,
            ..default()
        },
        Transform::from_xyz(4.0, 8.0, 4.0),
    ));
    commands.spawn(Camera3d::default());
}

fn update(mut state: ResMut<State>, mut camera: Query<&mut Transform, With<Camera3d>>) {
    let mut camera = camera.single_mut().unwrap();

    let t = Vec3::new(state.x, 0.0, 10.0);
    camera.translation = t;
    camera.look_at(t - Vec3::Z, Vec3::Y);

    state.x = 0.0;
}

[JMS55]

Approved with a small nit to improve the comment wording.