Improve clarity of WindowTextureNode and WindowSwapchainNode error messages (#1355)

Improve clarity of WindowTextureNode and WindowSwapchainNode error messages

Author: rmsc

crates/bevy_render/src/render_graph/nodes/window_swapchain_node.rs

@@ -49,7 +49,7 @@ impl Node for WindowSwapChainNode {
 
         let window = windows
             .get(self.window_id)
-            .expect("Received window resized event for non-existent window.");
+            .expect("Window swapchain node refers to a non-existent window.");
 
         let render_resource_context = render_context.resources_mut();
 

crates/bevy_render/src/render_graph/nodes/window_texture_node.rs

@@ -52,7 +52,7 @@ impl Node for WindowTextureNode {
 
         let window = windows
             .get(self.window_id)
-            .expect("Received window resized event for non-existent window.");
+            .expect("Window texture node refers to a non-existent window.");
 
         if self
             .window_created_event_reader