nixos/retroarch: add RetroArch as a desktop session

[j0hax]

Motivation for this change

Similar to kodi, this module allows users to launch a fullscreen RetroArch instance as the desktop.

Example

{
  # somewhere inside configuration.nix
  services.xserver.desktopManager.retroarch = {
    enable = true;
    package = pkgs.retroarchFull;
  };
}

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.05 Release Notes (or backporting 21.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review/3032/716

[SuperSandro2000]

Please add yourself as a maintainer. Should we add a test for this?

[j0hax]

I doubt a test is necessary for such a simple module, but I decided it doesn't hurt to have one anyways 😉

$ nix-build . -A nixosTests.retroarch
/nix/store/pg0i20h1g2xqxz9gpabp7kciwncf5idn-vm-test-run-retroarch