gauge: add fromManifest helper function

  nativeBuildInputs = [ gauge-unwrapped makeWrapper xorg.lndir ];

  passthru.withPlugins = f: gauge.override { plugins = f gaugePlugins; };

  passthru = {

    withPlugins = f: gauge.override { plugins = f gaugePlugins; };

    fromManifest = path:

      let

        manifest = lib.importJSON path;

        requiredPlugins = with manifest; [ Language ] ++ Plugins;

        manifestPlugins = plugins: map (name: plugins.${name} or (throw "Gauge plugin ${name} is not available!")) requiredPlugins;

      in gauge.withPlugins manifestPlugins;

  };

  inherit (gauge-unwrapped) meta;

}