Darwin gtk quartz follow up (#21883)

* gtk2-x11: Add gtk2 configuration with X11 backend

After making quartz the default for darwin, some builds started to fail since
they only support gtk with the X11 backend.

* apvlv: Use gtk2-x11 on darwin

* gpicview: Use gtk2-x11 for darwin

* lxappearance: Use gtk2-x11 for darwin

* fontforge-gtk: Use gtk2-x11 for darwin

* gbdfed: Use gtk2-x11 for darwin