set required-features for example light_textures & clustered_decals (#19913)

# Objective

- Example `light_textures` exit if feature `pbr_light_textures` is not
enabled. this is checked in code instead of using `required-features`
- Same for `clustered_decals` and `par_clustered_decals`
- Those examples are also using `eprintln`
- Those examples are using `process:exit` to exit

## Solution

- Use `required-features`
- Use logs
- Use `AppExit`

Author: mockersf

Cargo.toml

@@ -4426,6 +4426,7 @@ wasm = true
 name = "clustered_decals"
 path = "examples/3d/clustered_decals.rs"
 doc-scrape-examples = true
+required-features = ["pbr_clustered_decals"]
 
 [package.metadata.example.clustered_decals]
 name = "Clustered Decals"
@@ -4437,6 +4438,7 @@ wasm = false
 name = "light_textures"
 path = "examples/3d/light_textures.rs"
 doc-scrape-examples = true
+required-features = ["pbr_light_textures"]
 
 [package.metadata.example.light_textures]
 name = "Light Textures"

examples/3d/clustered_decals.rs

@@ -2,7 +2,6 @@
 
 use std::f32::consts::{FRAC_PI_3, PI};
 use std::fmt::{self, Formatter};
-use std::process;
 
 use bevy::{
     color::palettes::css::{LIME, ORANGE_RED, SILVER},
@@ -163,16 +162,10 @@ fn setup(
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<ExtendedMaterial<StandardMaterial, CustomDecalExtension>>>,
 ) {
-    // Error out if the clustered decals feature isn't enabled
-    if !cfg!(feature = "pbr_clustered_decals") {
-        eprintln!("Bevy was compiled without clustered decal support. Run with `--features=pbr_clustered_decals` to enable.");
-        process::exit(1);
-    }
-
     // Error out if clustered decals aren't supported on the current platform.
     if !decal::clustered::clustered_decals_are_usable(&render_device, &render_adapter) {
-        eprintln!("Clustered decals aren't usable on this platform.");
-        process::exit(1);
+        error!("Clustered decals aren't usable on this platform.");
+        commands.send_event(AppExit::error());
     }
 
     spawn_cube(&mut commands, &mut meshes, &mut materials);

examples/3d/light_textures.rs

@@ -2,7 +2,6 @@
 
 use std::f32::consts::{FRAC_PI_2, FRAC_PI_3, FRAC_PI_4, PI};
 use std::fmt::{self, Formatter};
-use std::process;
 
 use bevy::{
     color::palettes::css::{SILVER, YELLOW},
@@ -155,16 +154,10 @@ fn setup(
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
-    // Error out if the light textures feature isn't enabled
-    if !cfg!(feature = "pbr_light_textures") {
-        eprintln!("Bevy was compiled without light texture support. Run with `--features=pbr_light_textures` to enable.");
-        process::exit(1);
-    }
-
     // Error out if clustered decals (and so light textures) aren't supported on the current platform.
     if !decal::clustered::clustered_decals_are_usable(&render_device, &render_adapter) {
-        eprintln!("Light textures aren't usable on this platform.");
-        process::exit(1);
+        error!("Light textures aren't usable on this platform.");
+        commands.send_event(AppExit::error());
     }
 
     spawn_cubes(&mut commands, &mut meshes, &mut materials);