Fix intermittent drag-and-drop freezing on Windows

[zachbateman]

Objective

Fixes #19030.

Since Bevy 0.15.3, there has been a bug on Windows where drag-and-drop will occasionally freeze the application where the only fix is to resize the window.

Solution

This adds a check for any window events being received when determining if a redraw is requested—specifically on Windows. A drag-and-drop event sets the self.window_event_received flag to true.

For non-Windows platforms, self.redraw_requested(event_loop) is always called, but the Windows-specific branch has checks that for some reason sometimes don't properly handle a drag-and-drop event (and maybe other types of events?).

I also tried replacing all of the WINIT_WINDOWS.with_borrow(...) with just self.redraw_requested(event_loop), and that fixes the problem too (and then matches the non-Windows behavior), but I assume the Windows-specific checks are otherwise there for a reason.

Note: I'm not sure why the freeze only sometimes occurred. This change fixes the specific drag-and-drop freeze problem, but there may be some sort of deeper bug/issue causing the strange behavior in the first place.

Testing

I could replicate the intermittent freeze on Windows 11 in the drag-and-drop example, and this change seems to fully fix that problem.

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Showcase

Here is the existing intermittent freeze in action before the fix. While there is nothing in the drag-and-drop example window, the whole application is completely frozen until the window is resized.

Bevy.Drag.Drop.Bug_20250621.mp4

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