Disable Vsync for stress tests. (#5187)

# Objective

Currently stress tests are vsynced. This is undesirable for a stress test, as you want to run them with uncapped framerates.

## Solution

Ensure all stress tests are using PresentMode::Immediate if they render anything.

examples/stress_tests/many_cubes.rs

@@ -14,10 +14,15 @@ use bevy::{
     diagnostic::{FrameTimeDiagnosticsPlugin, LogDiagnosticsPlugin},
     math::{DVec2, DVec3},
     prelude::*,
+    window::PresentMode,
 };
 
 fn main() {
     App::new()
+        .insert_resource(WindowDescriptor {
+            present_mode: PresentMode::Immediate,
+            ..default()
+        })
         .add_plugins(DefaultPlugins)
         .add_plugin(FrameTimeDiagnosticsPlugin::default())
         .add_plugin(LogDiagnosticsPlugin::default())

examples/stress_tests/many_foxes.rs

@@ -4,6 +4,7 @@
 use bevy::{
     diagnostic::{FrameTimeDiagnosticsPlugin, LogDiagnosticsPlugin},
     prelude::*,
+    window::PresentMode,
 };
 
 struct Foxes {
@@ -16,6 +17,7 @@ fn main() {
     App::new()
         .insert_resource(WindowDescriptor {
             title: "🦊🦊🦊 Many Foxes! 🦊🦊🦊".to_string(),
+            present_mode: PresentMode::Immediate,
             ..default()
         })
         .add_plugins(DefaultPlugins)

examples/stress_tests/many_lights.rs

@@ -7,6 +7,7 @@ use bevy::{
     pbr::{ExtractedPointLight, GlobalLightMeta},
     prelude::*,
     render::{camera::ScalingMode, RenderApp, RenderStage},
+    window::PresentMode,
 };
 use rand::{thread_rng, Rng};
 
@@ -16,7 +17,7 @@ fn main() {
             width: 1024.0,
             height: 768.0,
             title: "many_lights".to_string(),
-            present_mode: bevy::window::PresentMode::Immediate,
+            present_mode: PresentMode::Immediate,
             ..default()
         })
         .add_plugins(DefaultPlugins)

examples/stress_tests/many_sprites.rs

@@ -9,6 +9,7 @@ use bevy::{
     math::Quat,
     prelude::*,
     render::camera::Camera,
+    window::PresentMode,
 };
 
 use rand::Rng;
@@ -17,6 +18,10 @@ const CAMERA_SPEED: f32 = 1000.0;
 
 fn main() {
     App::new()
+        .insert_resource(WindowDescriptor {
+            present_mode: PresentMode::Immediate,
+            ..default()
+        })
         // Since this is also used as a benchmark, we want it to display performance data.
         .add_plugin(LogDiagnosticsPlugin::default())
         .add_plugin(FrameTimeDiagnosticsPlugin::default())