There's one behavioral change here. Before this patch, if
`gtk-titlebar=false` we _never_ created a headerbar. This explicitly
contradicted the comments in the source, and the documentation for
`gtk-titlebar` imply that if a window starts out without a titlebar it
can be brought back later with the `toggle_window_decorations` keybind
action.
After this patch, a headerbar is always created, but if
`gtk-titlebar=false` or `window-decoration=false` it's immediately
hidden.
I'm not sure how this interacts with the current SSD/CSD detection that
seems to happen when running Ghostty on non-Gnome DEs so it'll be
important to get #4724 merged (plus any follow ups) to enable more
explicit control of SSD/CSD.
c4ece2a141