Implement GtkColorPicker for macOS
We can take insipiration from the existing implementation in GIMP3: https://gitlab.gnome.org/GNOME/gimp/-/blob/master/libgimpwidgets/gimppickbutton-quartz.c
We can take insipiration from the existing implementation in GIMP3: https://gitlab.gnome.org/GNOME/gimp/-/blob/master/libgimpwidgets/gimppickbutton-quartz.c