Add bevy_window::Window options for MacOS (#15820)

# Objective

MacOS has some nice options for controlling the window and titlebar to
make the content appear much more "immersively" in the window. This PR
exposes options for controlling this.

## Solution

Adds new fields to `Window` to control these, with doc comments to
explain what they do and that they're MacOS only.

## Testing

Tested on a MacOS machine (not my own, I don't have one). That's where
the below screenshots were taken.

---

## Showcase

On MacOS, you now have more options for configuring the window titlebar.
You can, for example, make the title bar transparent and only show the
window controls. This provides a more "immersive" experience for your
rendered content.

Before, only this was possible:
<img width="1392" alt="image"
src="https://github.com/user-attachments/assets/abf03da2-d247-4202-a7e7-731c45d80d54">

Now, you can create windows like this:
<img width="1392" alt="image2"
src="https://github.com/user-attachments/assets/3239d0e3-4708-4798-8755-188541e14f93">

This uses the following `bevy_window::Window` settings:
```rs
fullsize_content_view: true,
titlebar_transparent: true,
titlebar_show_title: false,
```

## Migration Guide

`bevy_window::Window` now has extra fields for configuring MacOS window
settings:
```rs
    pub movable_by_window_background: bool,
    pub fullsize_content_view: bool,
    pub has_shadow: bool,
    pub titlebar_shown: bool,
    pub titlebar_transparent: bool,
    pub titlebar_show_title: bool,
    pub titlebar_show_buttons: bool,
```

Using `Window::default` keeps the same behaviour as before.

crates/bevy_window/src/window.rs

@@ -314,6 +314,80 @@ pub struct Window {
     ///
     /// - Only used on iOS.
     pub recognize_pan_gesture: Option<(u8, u8)>,
+    /// Enables click-and-drag behavior for the entire window, not just the titlebar.
+    ///
+    /// Corresponds to [`WindowAttributesExtMacOS::with_movable_by_window_background`].
+    ///
+    /// # Platform-specific
+    ///
+    /// - Only used on macOS.
+    ///
+    /// [`WindowAttributesExtMacOS::with_movable_by_window_background`]: https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/macos/trait.WindowAttributesExtMacOS.html#tymethod.with_movable_by_window_background
+    pub movable_by_window_background: bool,
+    /// Makes the window content appear behind the titlebar.
+    ///
+    /// Corresponds to [`WindowAttributesExtMacOS::with_fullsize_content_view`].
+    ///
+    /// For apps which want to render the window buttons on top of the apps
+    /// itself, this should be enabled along with [`titlebar_transparent`].
+    ///
+    /// # Platform-specific
+    ///
+    /// - Only used on macOS.
+    ///
+    /// [`WindowAttributesExtMacOS::with_fullsize_content_view`]: https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/macos/trait.WindowAttributesExtMacOS.html#tymethod.with_fullsize_content_view
+    /// [`titlebar_transparent`]: Self::titlebar_transparent
+    pub fullsize_content_view: bool,
+    /// Toggles drawing the drop shadow behind the window.
+    ///
+    /// Corresponds to [`WindowAttributesExtMacOS::with_has_shadow`].
+    ///
+    /// # Platform-specific
+    ///
+    /// - Only used on macOS.
+    ///
+    /// [`WindowAttributesExtMacOS::with_has_shadow`]: https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/macos/trait.WindowAttributesExtMacOS.html#tymethod.with_has_shadow
+    pub has_shadow: bool,
+    /// Toggles drawing the titlebar.
+    ///
+    /// Corresponds to [`WindowAttributesExtMacOS::with_titlebar_hidden`].
+    ///
+    /// # Platform-specific
+    ///
+    /// - Only used on macOS.
+    ///
+    /// [`WindowAttributesExtMacOS::with_titlebar_hidden`]: https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/macos/trait.WindowAttributesExtMacOS.html#tymethod.with_titlebar_hidden
+    pub titlebar_shown: bool,
+    /// Makes the titlebar transparent, allowing the app content to appear behind it.
+    ///
+    /// Corresponds to [`WindowAttributesExtMacOS::with_titlebar_transparent`].
+    ///
+    /// # Platform-specific
+    ///
+    /// - Only used on macOS.
+    ///
+    /// [`WindowAttributesExtMacOS::with_titlebar_transparent`]: https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/macos/trait.WindowAttributesExtMacOS.html#tymethod.with_titlebar_transparent
+    pub titlebar_transparent: bool,
+    /// Toggles showing the window title.
+    ///
+    /// Corresponds to [`WindowAttributesExtMacOS::with_title_hidden`].
+    ///
+    /// # Platform-specific
+    ///
+    /// - Only used on macOS.
+    ///
+    /// [`WindowAttributesExtMacOS::with_title_hidden`]: https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/macos/trait.WindowAttributesExtMacOS.html#tymethod.with_title_hidden
+    pub titlebar_show_title: bool,
+    /// Toggles showing the traffic light window buttons.
+    ///
+    /// Corresponds to [`WindowAttributesExtMacOS::with_titlebar_buttons_hidden`].
+    ///
+    /// # Platform-specific
+    ///
+    /// - Only used on macOS.
+    ///
+    /// [`WindowAttributesExtMacOS::with_titlebar_buttons_hidden`]: https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/macos/trait.WindowAttributesExtMacOS.html#tymethod.with_titlebar_buttons_hidden
+    pub titlebar_show_buttons: bool,
 }
 
 impl Default for Window {
@@ -348,6 +422,13 @@ impl Default for Window {
             recognize_rotation_gesture: false,
             recognize_doubletap_gesture: false,
             recognize_pan_gesture: None,
+            movable_by_window_background: false,
+            fullsize_content_view: false,
+            has_shadow: true,
+            titlebar_shown: true,
+            titlebar_transparent: false,
+            titlebar_show_title: true,
+            titlebar_show_buttons: true,
         }
     }
 }

crates/bevy_winit/src/winit_windows.rs

@@ -127,6 +127,19 @@ impl WinitWindows {
                 winit_window_attributes.with_skip_taskbar(window.skip_taskbar);
         }
 
+        #[cfg(target_os = "macos")]
+        {
+            use winit::platform::macos::WindowAttributesExtMacOS;
+            winit_window_attributes = winit_window_attributes
+                .with_movable_by_window_background(window.movable_by_window_background)
+                .with_fullsize_content_view(window.fullsize_content_view)
+                .with_has_shadow(window.has_shadow)
+                .with_titlebar_hidden(!window.titlebar_shown)
+                .with_titlebar_transparent(window.titlebar_transparent)
+                .with_title_hidden(!window.titlebar_show_title)
+                .with_titlebar_buttons_hidden(!window.titlebar_show_buttons);
+        }
+
         let display_info = DisplayInfo {
             window_physical_resolution: (
                 window.resolution.physical_width(),