RenderLayers performance drop

When increasing the number of RenderLayers and spawning one Camera3d per layer,
performance drops significantly, even in minimal scenes.

In the following test(based on examples/3d/3d_scene), where only one camera sees the spwaned cube (RenderLayers 0) , I measure:
```html
Layers | Cameras | FPS
1 | 1 | ~900
2 | 2 | ~720
5 | 5 | ~425
10 | 10 | ~270
```
test:
```rust
//! A simple 3D scene with light shining over a cube sitting on a plane.

use bevy::{
prelude::*,
render::view::RenderLayers,
window::PresentMode,
};

#[derive(Resource)]
pub struct FpsTimer(pub Timer);

const ADDITIONAL_LAYERS:usize = 1;

fn main() {
App::new()
.add_plugins(DefaultPlugins
.set(WindowPlugin {
primary_window: Some(Window {
#[cfg(not(target_os = "android"))]
present_mode: PresentMode::Immediate,
#[cfg(target_os = "android")]
present_mode: PresentMode::Fifo,
..Default::default()
}),
..Default::default()
})
)
.add_systems(Startup, setup)
.add_systems(Update,
fps_counter,
)
.run();
}

/// set up a simple 3D scene
fn setup(
mut commands: Commands,
mut meshes: ResMut>,
mut materials: ResMut>,
) {

// cube
commands.spawn((
Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
MeshMaterial3d(materials.add(Color::srgb_u8(124, 144, 255))),
Transform::from_xyz(0.0, 0.5, 0.0),
RenderLayers::layer(0),
));
// light
commands.spawn((
PointLight {
//shadows_enabled: true,
..default()
},
Transform::from_xyz(4.0, 8.0, 4.0),
));
// camera
commands.spawn((
Camera {
order: 0,
..default()
},
Camera3d::default(),
Transform::from_xyz(-2.5, 4.5, 9.0).looking_at(Vec3::ZERO, Vec3::Y),
RenderLayers::layer(0),
));

for i in 0..ADDITIONAL_LAYERS {
commands.spawn((
Camera {
order: (i+1) as _,
..default()
},
Camera3d::default(),
Transform::from_xyz(-2.5, 4.5, 9.0).looking_at(Vec3::ZERO, Vec3::Y),
RenderLayers::layer((i+1) as _),
));
}

commands.insert_resource(FpsTimer(Timer::from_seconds(1.0, TimerMode::Repeating)));
}

pub fn fps_counter(time: Res, mut timer: ResMut) {
timer.0.tick(time.delta());
if timer.0.finished() {
println!("FPS: {}", 1.0 / time.delta_secs());
}
}
```