Upgrade `winit`/`raw-window-handle` to latest version

[hannobraun]

We currently depend on raw-window-handle 0.4.3. As of this writing, the latest version is 0.5.0.

Upgrading is currently blocked on winit 0.27.0 being published (rust-windowing/winit#2376), and wgpu (which doesn't seem to have started the upgrade).

[hannobraun]

No longer blocked on winit. Still blocked on wgpu, which has an open pull request now (gfx-rs/wgpu#2918). Updated the issue title accordingly.

[hannobraun]

Winit 0.27.2 supports raw-window-handle 0.4, which means it should work with wgpu. No longer blocked!

[hannobraun]

Closing in favor of #976.