winit: MacOS can't wake up during resize, breaks timeout schemes

As the comment describes, nextEventMatchingMask:untilDate:inMode:dequeue: blocks during a resize and does not return events until the resize is complete. That includes not returning events sent via postEvent:atStart:, which means Proxy::wakeup() doesn’t actually cause run_forever() to wake up.

This property is especially unfortunate with glutin_window, which implements its own fn wait_event_timeout(&mut self, timeout: Duration) by calling run_forever() and interrupting when the timeout expires. Since it can’t interrupt, a wait_event_timeout() that wants to yield 60 fps to e.g. drive a render loop will simply hang entirely until the user is done resizing.

I’ve been experimenting with ways to get nextEventMatchingMask: to be less thorny, but another complimentary approach would be to expose a new run_until_timeout() call in addition to poll_events() and run_forever() – or perhaps to deprecate poll_events() and run_forever() in favor of run_until_timeout(Some(0)) and run_until_timeout(None). A timeout-aware API would let glutin_window pass its deadline all the way down to nextEventMatchingMask:untilDate:, avoid spawning needless timeout threads, and sidestep some of the resize-related blocking issues all at once.