Use current_exe for default window title (#18553)

# Objective

- We currently default to "App" for the window title, it would be nice
if examples had more descriptive names

## Solution

- Use `std::env::current_exe` to try to figure out a default title. If
it's not present. Use "App".

## Testing

- I tested that examples that set a custom title still use the custom
title and that examples without a custom title use the example name

---

### Showcase

Here's the 3d_scene example:


![image](https://github.com/user-attachments/assets/bc67edc7-4211-4479-a027-ee6c52b0bd02)

### Notes

Here's a previous attempt at this from a few years ago
https://github.com/bevyengine/bevy/pull/3404

There's some relevant discussion in there, but cart's decision was to
default to "App" when no name was found.

---------

Co-authored-by: Zachary Harrold <zac@harrold.com.au>

crates/bevy_window/src/window.rs

@@ -1,4 +1,4 @@
-use alloc::{borrow::ToOwned, string::String};
+use alloc::{borrow::ToOwned, format, string::String};
 use core::num::NonZero;
 
 use bevy_ecs::{
@@ -6,6 +6,7 @@ use bevy_ecs::{
     prelude::Component,
 };
 use bevy_math::{CompassOctant, DVec2, IVec2, UVec2, Vec2};
+use bevy_platform_support::sync::LazyLock;
 use log::warn;
 
 #[cfg(feature = "bevy_reflect")]
@@ -19,6 +20,24 @@ use bevy_reflect::{ReflectDeserialize, ReflectSerialize};
 
 use crate::VideoMode;
 
+/// Default string used for the window title.
+///
+/// It will try to use the name of the current exe if possible, otherwise it defaults to "App"
+static DEFAULT_WINDOW_TITLE: LazyLock<String> = LazyLock::new(|| {
+    #[cfg(feature = "std")]
+    {
+        std::env::current_exe()
+            .ok()
+            .and_then(|current_exe| Some(format!("{}", current_exe.file_stem()?.to_string_lossy())))
+            .unwrap_or_else(|| "App".to_owned())
+    }
+
+    #[cfg(not(feature = "std"))]
+    {
+        "App".to_owned()
+    }
+});
+
 /// Marker [`Component`] for the window considered the primary window.
 ///
 /// Currently this is assumed to only exist on 1 entity at a time.
@@ -429,7 +448,7 @@ pub struct Window {
 impl Default for Window {
     fn default() -> Self {
         Self {
-            title: "App".to_owned(),
+            title: DEFAULT_WINDOW_TITLE.to_owned(),
             name: None,
             cursor_options: Default::default(),
             present_mode: Default::default(),