macOS: focus is moved to first split when toggling non-native fullscreen

[mitchellh]

Discussed in #6997

^{Originally posted by frangio April 4, 2025}
This appears to have been fixed before in #405 but I'm seeing it in 1.1.3 with non-native fullscreen in macOS Sequoia 15.3.2.

Reproduction

macos-non-native-fullscreen = true

1. Start Ghostty
2. Cmd+D to create right split, focus is on right
3. Cmd+Enter to fullscreen (non-native)

Observe: focus is on the left split

This only happens with non-native fullscreen