Migrate fog volumes to required components (#15568)

# Objective

Another part of the migration to required components: fog volumes!

## Solution

Deprecate `FogVolumeBundle` and make `FogVolume` require `Transform` and
`Visibility`, as per the [chosen
proposal](https://hackmd.io/@bevy/required_components/%2FcO7JPSAQR5G0J_j5wNwtOQ).

---

## Migration Guide

Replace all insertions of `FogVolumeBundle` with the `Visibility`
component. The other components required by it will now be inserted
automatically.

crates/bevy_pbr/src/volumetric_fog/mod.rs

@@ -29,6 +29,8 @@
 //!
 //! [Henyey-Greenstein phase function]: https://www.pbr-book.org/4ed/Volume_Scattering/Phase_Functions#TheHenyeyndashGreensteinPhaseFunction
 
+#![expect(deprecated)]
+
 use bevy_app::{App, Plugin};
 use bevy_asset::{load_internal_asset, Assets, Handle};
 use bevy_color::Color;
@@ -121,6 +123,10 @@ pub type VolumetricFogSettings = VolumetricFog;
 /// A convenient [`Bundle`] that contains all components necessary to generate a
 /// fog volume.
 #[derive(Bundle, Clone, Debug, Default)]
+#[deprecated(
+    since = "0.15.0",
+    note = "Use the `FogVolume` component instead. Inserting it will now also insert the other components required by it automatically."
+)]
 pub struct FogVolumeBundle {
     /// The actual fog volume.
     pub fog_volume: FogVolume,
@@ -139,6 +145,7 @@ pub struct FogVolumeBundle {
 
 #[derive(Clone, Component, Debug, Reflect)]
 #[reflect(Component, Default, Debug)]
+#[require(Transform, Visibility)]
 pub struct FogVolume {
     /// The color of the fog.
     ///

examples/3d/volumetric_fog.rs

@@ -4,7 +4,7 @@ use bevy::{
     color::palettes::css::RED,
     core_pipeline::{bloom::Bloom, tonemapping::Tonemapping, Skybox},
     math::vec3,
-    pbr::{FogVolumeBundle, VolumetricFog, VolumetricLight},
+    pbr::{FogVolume, VolumetricFog, VolumetricLight},
     prelude::*,
 };
 
@@ -122,10 +122,10 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>, app_settings: R
     ));
 
     // Add the fog volume.
-    commands.spawn(FogVolumeBundle {
-        transform: Transform::from_scale(Vec3::splat(35.0)),
-        ..default()
-    });
+    commands.spawn((
+        FogVolume::default(),
+        Transform::from_scale(Vec3::splat(35.0)),
+    ));
 
     // Add the help text.
     commands.spawn(