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?
saveComments: false,
    defines: bundleDefines,
    map: {
      "pdfjs-lib": "../pdf",
    },
  };
  const licenseHeaderLibre = fs
    .readFileSync("./src/license_header_libre.js")
    .toString();
  const preprocessor2 = require("./external/builder/preprocessor2.js");
  return inputStream
    .pipe(transform("utf8", preprocess))
    .pipe(gulp.dest(outputDir));
}
function buildLib(defines, dir) {
  const versionInfo = getVersionJSON();
  const bundleDefines = builder.merge(defines, {
    BUNDLE_VERSION: versionInfo.version,
    BUNDLE_BUILD: versionInfo.commit,
    TESTING: defines.TESTING || process.env.TESTING === "true",
    DEFAULT_PREFERENCES: getDefaultPreferences(
      defines.SKIP_BABEL ? "lib/" : "lib-legacy/"
    ),
  });
  const inputStream = merge([
    gulp.src(
      [
        "src/{core,display,shared}/**/*.js",
        "!src/shared/{cffStandardStrings,fonts_utils}.js",
        "src/{pdf,pdf.worker}.js",