Reactive RunMode broken on Windows 10

[parasyte]

This was reported in #21 (comment)

git bisect shows that 04b3921 caused the regression. (Looks like my guess was right!)

To Reproduce
Steps to reproduce the behavior:

1. Run egui_demo_app on Windows 10
2. Open the Backend panel.
3. Set "Mode" to Reactive

Expected behavior
With the Backend panel open, the "Total frames painted" counter should not be updated until an event is produced. E.g. by moving the mouse.

Desktop (please complete the following information):

• OS: Windows 10
• Version: master

[parasyte]

FWIW, rfd has async file dialogs that work correctly with the current winit event loop. This has been discussed in multiple places, including rust-windowing/winit#1779 and EmbarkStudios/nfd2#11

[emilk]

Yeah, it is looking more and more like we should revert 04b3921

I'd still love for non-async dialogs to work as well.

I'll take a look at the winit fix provided by @PolyMeilex at https://github.com/PolyMeilex/winit (and ported to winit 0.25 by @vihdzp at https://github.com/OfficialURL/winit)