Read back full screen state from window on macOS

[coreh]

Objective

I'm trying to display on a menu screen of my game the Windowed/Full screen state. However, on macOS it's possible for the user to trigger borderless fullscreen directly from the window controls, which results in a stale/wrong state displayed.

Solution

• Add logic to read back full screen state and apply it to the window when the user directly makes it full screen via the window controls on macOS

Testing

• Did you test these changes? If so, how? Yes, mostly on my game
• Are there any parts that need more testing? I'm not sure if this has performance implications, as the call might be blocking on the UI thread. However, unscientifically I didn't notice any degradation.
• How can other people (reviewers) test your changes? Is there anything specific they need to know? Adding log statements to the match branches should suffice.
• If relevant, what platforms did you test these changes on, and are there any important ones you can't test? Just macOS

[mockersf]

does winit sends a resolution changed event (or another one) when the user changes the window controls? I think it would be better to add this when the window reacts to a corresponding event from winit

[tychedelia]

We should probably make sure we are copying the correct monitor returned from winit rather than just defaulting to Current.

[alice-i-cecile]

Should we be upstreaming this fix to winit instead?