winit: Fix preferred window size not being taken into account when it changes multiple times between window creation and the resize event received from the window manager

In this phase between the window being resized and receiving the resize event, the pending_requested_size variable tracks the value to be used in adjust_window_size_to_satisfy_constraints. Unfortunately,
it was never set.

Amends commit 1c73144b09.

Fixes #8452

internal/backends/winit/winitwindowadapter.rs

@@ -604,6 +604,7 @@ impl WinitWindowAdapter {
                     self.resize_event(size)?;
                     Ok(true)
                 } else {
+                    self.pending_requested_size.set(size.into());
                     // None means that we'll get a `WindowEvent::Resized` later
                     Ok(false)
                 }
@@ -629,6 +630,7 @@ impl WinitWindowAdapter {
         if size.width > 0 && size.height > 0 {
             let physical_size = physical_size_to_slint(&size);
             self.size.set(physical_size);
+            self.pending_requested_size.set(None);
             let scale_factor = WindowInner::from_pub(self.window()).scale_factor();
             self.window().try_dispatch_event(WindowEvent::Resized {
                 size: physical_size.to_logical(scale_factor),