152: Update to latest winit (0.20.0-alpha6) r=kvark a=grovesNL
Updated to latest winit to fix examples:
- `RedrawRequested` is now used for rendering
- `EventsCleared` replaced by `MainEventsCleared` which requests redraw
- Removed Metal auto-capture and escape key handling from hello-triangle to simplify the example slightly (it doesn't use `framework`, so we should try to make it as simple as possible IMO)
Should we also remove the `feature = gl` parts of the examples to simplify them until GL is reenabled?
Co-authored-by: Joshua Groves <josh@joshgroves.com>