nixos/cinnamon: Replace xplayer with celluloid

- Cinnamon has been updated to 6.4, please check the [upstream announcement](https://www.linuxmint.com/rel_xia_whatsnew.php) for more details.

  - Following [changes in Mint 22](https://github.com/linuxmint/mintupgrade/commit/f239cde908288b8c250f938e7311c7ffbc16bd59) we are no longer overriding Qt application styles. You can still restore the previous default with `qt.style = "gtk2"` and `qt.platformTheme = "gtk2"`.

  - Following [changes in Mint 20](https://github.com/linuxmint/mintupgrade-legacy/commit/ce15d946ed9a8cb8444abd25088edd824bfb18f6) we are replacing xplayer with celluloid since xplayer is no longer maintained.

- Xfce has been updated to 4.20, please check the [upstream feature tour](https://www.xfce.org/about/tour420) for more details.

  - Wayland session is still [experimental](https://wiki.xfce.org/releng/wayland_roadmap) and requires opt-in using `enableWaylandSession` option.

        xviewer

        xreader

        xed-editor

        xplayer

        pix

        # external apps shipped with linux-mint

        celluloid

        gnome-calculator

        gnome-calendar

        gnome-screenshot