cosmic: add orca (screen reader) support (#417847)

nixos/modules/services/desktop-managers/cosmic.nix

···
 
 let
   cfg = config.services.desktopManager.cosmic;
+  notExcluded = pkg: utils.disablePackageByName pkg config.environment.cosmic.excludePackages;
   excludedCorePkgs = lib.lists.intersectLists corePkgs config.environment.cosmic.excludePackages;
   # **ONLY ADD PACKAGES WITHOUT WHICH COSMIC CRASHES, NOTHING ELSE**
   corePkgs =
···
     services.avahi.enable = lib.mkDefault true;
     services.gnome.gnome-keyring.enable = lib.mkDefault true;
     services.gvfs.enable = lib.mkDefault true;
+    services.orca.enable = lib.mkDefault (notExcluded pkgs.orca);
     services.power-profiles-daemon.enable = lib.mkDefault (
       !config.hardware.system76.power-daemon.enable
     );

pkgs/by-name/co/cosmic-session/package.nix

···
     "target/${stdenv.hostPlatform.rust.cargoShortTarget}"
   ];
 
-  env.XDP_COSMIC = "${xdg-desktop-portal-cosmic}/libexec/xdg-desktop-portal-cosmic";
+  env = {
+    XDP_COSMIC = lib.getExe xdg-desktop-portal-cosmic;
+    ORCA = "orca"; # get orca from $PATH
+  };
 
   passthru = {
     providedSessions = [ "cosmic" ];