Refs #8975 -- Add return to RenderDevice::poll() (#8977)

# Objective
Fixes #8975

## Solution
Return the value from wgpu::device::poll().

---

## Changelog
In render_device.rs
- RenderDevice::Poll()

crates/bevy_render/src/renderer/render_device.rs

@@ -50,10 +50,16 @@ impl RenderDevice {
 
     /// Check for resource cleanups and mapping callbacks.
     ///
+    /// Return `true` if the queue is empty, or `false` if there are more queue
+    /// submissions still in flight. (Note that, unless access to the [`wgpu::Queue`] is
+    /// coordinated somehow, this information could be out of date by the time
+    /// the caller receives it. `Queue`s can be shared between threads, so
+    /// other threads could submit new work at any time.)
+    ///
     /// no-op on the web, device is automatically polled.
     #[inline]
-    pub fn poll(&self, maintain: wgpu::Maintain) {
-        self.device.poll(maintain);
+    pub fn poll(&self, maintain: wgpu::Maintain) -> bool {
+        self.device.poll(maintain)
     }
 
     /// Creates an empty [`CommandEncoder`](wgpu::CommandEncoder).