Change present mode on many_buttons and many_glyphs from Immediate to…

… AutoNoVsync (bevyengine#8681)

# Objective

Fix the examples many_buttons and many_glyphs not working on the WebGPU
examples page. Currently they both fail with the follow error:

```
panicked at 'Only FIFO/Auto* is supported on web', ..../wgpu-0.16.0/src/backend/web.rs:1162:13
```

## Solution

Change `present_mode` from `PresentMode::Immediate` to
`PresentMode::AutoNoVsync`. AutoNoVsync seems to be common mode used by
other examples of this kind.

examples/stress_tests/many_buttons.rs

@@ -25,7 +25,7 @@ fn main() {
 
     app.add_plugins(DefaultPlugins.set(WindowPlugin {
         primary_window: Some(Window {
-            present_mode: PresentMode::Immediate,
+            present_mode: PresentMode::AutoNoVsync,
             ..default()
         }),
         ..default()

examples/stress_tests/many_glyphs.rs

@@ -16,7 +16,7 @@ fn main() {
     let mut app = App::new();
     app.add_plugins(DefaultPlugins.set(WindowPlugin {
         primary_window: Some(Window {
-            present_mode: PresentMode::Immediate,
+            present_mode: PresentMode::AutoNoVsync,
             ..default()
         }),
         ..default()