macOS: Introduce config to hide Ghostty from the dock and cmd-tab

[mitchellh]

Discussed in #3810

^{Originally posted by frolvanya December 28, 2024}

I'm using ghostty primarily in quick-terminal mode, so I don't want to see an icon in the dock

Proposal

Introduce a new configuration macos-hidden (boolean). When set to true, the Ghostty app will be hidden. I think concretely, this means turning the app into an "accessory" app:

NSApp.setActivationPolicy(.accessory)

This has a number of downsides, so it must be carefully documented. Notably:

• App no longer appears in dock
• App no longer appears in cmd-tab
• Looks like keyboard layout changes are no longer automatic

I think as a future improvement we can introduce a menu bar icon that can bring the app to focus when click (optional). But introducing this option as default false will help get some quick-terminal-only users going more happily.

[mitchellh]

Note this Raycast behavior we may want to look into as well: #3810 (comment)