Bundle Fractal for macOS

I've started to bundle Fractal for macOS (MR incoming), and here is (roughly) what needs to be done. I already done most of the "hard" things, it is just not pushed yet.

• configure meson to install the binary in an .app bundle (--prefix /path/to/Fractal.app/Contents --bindir MacOS)
• have an .icns version of the icon
• have an Info.plist with the app informations (app name/version/description, copyright stuff, …)
• find all dependencies (gtk, cairo, pango, …) and:
  • copy them inside the bundle (Fractal.app/Contents/Framework/)
  • fix the library search path of both the fractal binary and the libraries to link to the bundled dylibs
  • do that recursivly
• copy everything GTK/gdk/whatever might need (Adwaita, macOS theme (keybindings), glib compiled schemas, gdk things… might not be complete)
• inject somehow environment variables
  • GDK_PIXBUF_MODULE_FILE=/path/to/Fractal.app/Contents/Resources/whatever/loaders.cache for the pixbuf loaders cache, generated by gdk-pixbuf-query-loaders
  • GTK_IM_MODULE_FILE=/path/to/Fractal.app/Contents/Resources/whatever/gtk.immodules for the GTK input method modules list, generated by gtk-query-immodules-3.0
  • XDG_DATA_DIRS=/path/to/Fractal.app/Contents/Resources/whatever for things like the theme, icons, glib's schemas, …
  • XDG_CONFIG_DIRS=/path/to/Fractal.app/Contents/Resources/whatever for the GTK settings (saying at least to use Adwaita)
  • maybe more? I might have missed something
• sign the binaries (or else it won't launch without disabling security stuff on the mac), which means the wrapper that injects the environment variables has to be a binary (you can't sign a shell script)
• fix things like HiDPI not working properly
• have it built in CI (needs a runner running macOS)
• open a lot of issues in GTK because it is pretty much broken (but usable) on macOS
• build a DMG as an "installer"
• reduce the app bundle by striping resources we don't need (we don't need the whole Adwaita theme for example)
• provide alternatives for things depending on Dbus¹ and Freedesktop things (like libsecret, opening files/URLs, …)

1. We can't depend on Dbus for anything critical. If a feature isn't available because Dbus and/or some services aren't running, it might be OK, but having a feature displayed but not working is worst. ↩