Make RawHandleWrapper fields private to save users from themselves (#16968)

# Objective

Fixes #16683

## Solution

Make all fields ine `RawHandleWrapper` private.

## Testing

- CI
- `cargo clippy`
- The lightmaps example
---

## Migration Guide

The `window_handle` and `dispay_handle` fields on `RawHandleWrapper` are
no longer public. Use the newly added getters and setters to manipulate
them instead.

crates/bevy_render/src/view/window/mod.rs

@@ -322,8 +322,8 @@ pub fn create_surfaces(
             .entry(window.entity)
             .or_insert_with(|| {
                 let surface_target = SurfaceTargetUnsafe::RawHandle {
-                    raw_display_handle: window.handle.display_handle,
+                    raw_display_handle: window.handle.get_display_handle(),
-                    raw_window_handle: window.handle.window_handle,
+                    raw_window_handle: window.handle.get_window_handle(),
                 };
                 // SAFETY: The window handles in ExtractedWindows will always be valid objects to create surfaces on
                 let surface = unsafe {

crates/bevy_window/src/raw_handle.rs

@@ -49,9 +49,9 @@ impl<W: 'static> Deref for WindowWrapper<W> {
 pub struct RawHandleWrapper {
     _window: Arc<dyn Any + Send + Sync>,
     /// Raw handle to a window.
-    pub window_handle: RawWindowHandle,
+    window_handle: RawWindowHandle,
     /// Raw handle to the display server.
-    pub display_handle: RawDisplayHandle,
+    display_handle: RawDisplayHandle,
 }
 
 impl RawHandleWrapper {
@@ -75,6 +75,41 @@ impl RawHandleWrapper {
     pub unsafe fn get_handle(&self) -> ThreadLockedRawWindowHandleWrapper {
         ThreadLockedRawWindowHandleWrapper(self.clone())
     }
+
+    /// Gets the stored window handle.
+    pub fn get_window_handle(&self) -> RawWindowHandle {
+        self.window_handle
+    }
+
+    /// Sets the window handle.
+    ///
+    /// # Safety
+    ///
+    /// The passed in [`RawWindowHandle`] must be a valid window handle.
+    // NOTE: The use of an explicit setter instead of a getter for a mutable reference is to limit the amount of time unsoundness can happen.
+    //       If we handed out a mutable reference the user would have to maintain safety invariants throughout its lifetime. For consistency
+    //       we also prefer to handout copies of the handles instead of immutable references.
+    pub unsafe fn set_window_handle(&mut self, window_handle: RawWindowHandle) -> &mut Self {
+        self.window_handle = window_handle;
+
+        self
+    }
+
+    /// Gets the stored display handle
+    pub fn get_display_handle(&self) -> RawDisplayHandle {
+        self.display_handle
+    }
+
+    /// Sets the display handle.
+    ///
+    /// # Safety
+    ///
+    /// The passed in [`RawDisplayHandle`] must be a valid display handle.
+    pub fn set_display_handle(&mut self, display_handle: RawDisplayHandle) -> &mut Self {
+        self.display_handle = display_handle;
+
+        self
+    }
 }
 
 // SAFETY: [`RawHandleWrapper`] is just a normal "raw pointer", which doesn't impl Send/Sync. However the pointer is only