Update and unbundle dependencies
    
    - libnotify is replaced by GDBus calls;
    - libcanberra is replaced by system calls to canberra-gtk-play;
    - dbus-glib is replaced by GDBus;
    - libapplication-gtk3 is only used in conjunction with gtk3;
    - libdeflate, libpsl, and miniupnpc system versions are preferred,
      only falling back to bundled versions when absent;
    - fast_float, libb64, and utf8cpp can be unbundled and built with
      system versions;
    - fmt cannot be unbundled yet as the code is incompatible with fmt-10;
    - Declare bundled provides for dependencies which are still needed.