KinematicCharacterController Velocity is dependent on framerate.

The Velocity component is updated by bevy_rapier even for KinematicCharacterController/Rigidbody::KinematicPositionBased. Unfortunately, the reported velocity is tied to the framerate! Higher delta times results in a higher velocity.

This example (using Bevy 0.12 and bevy_rapier2d 0.24) shows what happens if we artificially decrease the framerate (by enabling the `laggy` system:
```rust
use std::time::Duration;

use bevy::{prelude::*, render::camera::ScalingMode};
use bevy_rapier2d::prelude::*;

fn main() {
App::new()
.add_plugins(DefaultPlugins)
.add_plugins(RapierPhysicsPlugin::::pixels_per_meter(350.0))
.add_plugins(RapierDebugRenderPlugin::default())
.add_systems(Startup, spawn_collider)
.add_systems(Update, set_move)
.add_systems(PostUpdate, print_velocity.after(PhysicsSet::Writeback))
// .add_systems(Update, laggy) // Uncomment for lag!
.run();
}

fn spawn_collider(mut commands: Commands) {
commands
.spawn(SpatialBundle::default())
.insert(Collider::cuboid(100.0, 100.0))
.insert(RigidBody::KinematicPositionBased)
.insert(Velocity::default())
.insert(KinematicCharacterController::default());

commands.spawn(Camera2dBundle {
projection: OrthographicProjection {
near: -1000.0,
far: 1000.0,
scaling_mode: ScalingMode::FixedVertical(700.0),
..Default::default()
},
..Default::default()
});
}

fn laggy() {
std::thread::sleep(Duration::from_millis(100));
}

fn set_move(time: Res, mut controllers: Query<&mut KinematicCharacterController>) {
for mut controller in controllers.iter_mut() {
controller.translation = Some(Vec2::NEG_X * 50.0 * time.delta_seconds());
}
}

fn print_velocity(velocities: Query<&Velocity>) {
dbg!(velocities.single());
}
```
My results: Without the `laggy` system, my velocity is ~50. With the `laggy` system, my velocity is >300.

My concrete use case for the Velocity component on a KinematicCharacterController is a generic camera. I want my camera to be able to follow any entity and I also want the camera to "look ahead" of where the entity is going. I do this by adding the entity's velocity (multiplied by some "prediction time") to the entity's position and lerping the camera there. Ideally I want this system to work for physics objects or kinematic characters or whatever else. Unfortunately this breaks with kinematic characters because of this bug.