Recently we upgraded to Gulp 4. However, the following things still need to be addressed in some way:

- If a task series is executed with an anonymous function inside it, we'll see `Starting '<anonymous>'` in the output, which isn't that great. We need to either suppress it or use named functions.
- If a task is private, it should be hidden in some way. For example, `gh-pages-prepare` is only used in the public `web` target and should not be used on its own, however currently it shows in the default `gulp` output since it's a regular task. Perhaps we should mark them with an underscore?
const pdfFile = fs.readFileSync(dir + "/build/pdf.js").toString();
  const pdfWorkerFile = fs
    .readFileSync(dir + "/build/pdf.worker.js")
    .toString();
  const pdfSandboxFile = fs
    .readFileSync(dir + "/build/pdf.sandbox.js")
    .toString();
  const pdfImageDecodersFile = fs
    .readFileSync(dir + "/image_decoders/pdf.image_decoders.js")
    .toString();
  const viewerFiles = {
    "pdf.js": pdfFile,
    "viewer.js": fs.readFileSync(dir + "/web/viewer.js").toString(),
  };
  console.log();
  console.log("### Minifying js files");
  const Terser = require("terser");
  const options = {