This fixes#786 by adding a check to the callback that unhides the menu
bar to only unhide the menu bar if focus was lost to another Ghostty
window.
That's the desired behaviour: when focus is lost to another app's
window, we want the non-native-fullscreen window to stay unchanged in
background, but when changing focus to another Ghostty window, we want
to unhide the menu bar.
Why did this problem even show up?
It started to show up with the introduction of the Xib-file based
approach, in 3018377.
Before that, in 27ddc90, for example, the app would receive the same
notifications, but the `.autoHideMenuBar` didn't have an effect on the
window. Only after adding the Xib-file did it start to have an effect.
So I figured there's two ways we could fix it:
1. Figure out why the `.autoHideMenuBar` now works with Xib-files and
suppress it, or
2. Encode in the code the behaviour that we actually want: we only want
to show the menu bar when focus shifts to another one of Ghostty's
windows, but we want to leave it untouched when focus is lost to
another app's window.
I went with (2) but I think (1) is also valid and happy to close PR if
that's what we want to do.
The macOS desktop menu-bar grows in total height by adding extra padding
to deal with the physical notch found on various MacBook displays.
When config `macos-non-native-fullscreen = visible-menu` we apply
`safeAreaInsets.top` to reduce frame height.
