fix: Use BorderlessFullscreen instead of true fullscreen (fix alt+tab)

[MaxCWhitehead]

Using borderless fullscreen mode fixes alt tab not working in fullscreen. Probably should support both - but this seems like a preferable default.

One side effect I see in jumpy is that when fullscreen on high res display the UI scaling no longer gets tiny (now looks as I'd expect). I'd show screenshots to compare, but the screenshot tool on macOS doesn't work in true fullscreen mode either 😉

Any concerns with this?

[zicklag]

My only thought is that on Linux with gnome there was a weird thing at some point where you could only get full-performance without random skips by running in exclusive full screen. But I'm not sure if that's an issue anymore or if they fixed it, so probably not worth dodging it at the moment.

If we were some super high-performance game it might be worth having an exclusive fullscreen option, because I think it's good for performance, because I think it can skip the system compositor, but we're probably good.