Fix egui-wgpu performance regression (#3580)

Introduced in the recent multi-viewports work, we accidentally recreated
the wgpu surfaces every frame. This is now fixed.

I found this while improving the profiling of `eframe`

crates/egui_glow/examples/pure_glow.rs

@@ -235,7 +235,7 @@ fn main() {
                     gl_window.resize(**new_inner_size);
                 }
 
-                let event_response = egui_glow.on_event(&event);
+                let event_response = egui_glow.on_window_event(&event);
 
                 if event_response.repaint {
                     gl_window.window().request_redraw();