Auto merge of #23497 - jdm:windows-resize, r=asajeffrey

Fix behaviour of window resizing on Windows.

This makes Windows builds usable when the window is resized.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #23489
- [x] These changes do not require tests because we can't run tests on Windows CI yet.

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components/compositing/compositor.rs

@@ -663,6 +663,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
         }
 
         self.send_window_size(WindowSizeType::Resize);
+        self.composite_if_necessary(CompositingReason::Resize);
     }
 
     pub fn on_mouse_window_event_class(&mut self, mouse_window_event: MouseWindowEvent) {
@@ -1566,4 +1567,6 @@ pub enum CompositingReason {
     NewWebRenderFrame,
     /// WebRender has processed a scroll event and has generated a new frame.
     NewWebRenderScrollFrame,
+    /// The window has been resized and will need to be synchronously repainted.
+    Resize,
 }