On Windows, fix RedrawRequested delivery

When calling `Window::request_redraw` from the `RedrawRequested`
handler the `RedrawWindow` won't result in `WM_PAINT` being delivered
due since user callback is run before `DefWindowProcW` is called.

Track whether the user called `Window::request_redraw` and ask for
`RedrawWindow` after running the said function during `WM_PAINT`
handling.

Fixes #3150.

src/platform_impl/windows/window.rs

@@ -149,6 +149,8 @@ impl Window {
 
     #[inline]
     pub fn request_redraw(&self) {
+        // NOTE: mark that we requested a redraw to handle requests during `WM_PAINT` handling.
+        self.window_state.lock().unwrap().redraw_requested = true;
         unsafe {
             RedrawWindow(self.hwnd(), ptr::null(), 0, RDW_INTERNALPAINT);
         }