This is very confusing as seen in #12974 or #12906. My suggestion would be "legacy."
return merge([
    createComponentsBundle(defines).pipe(gulp.dest(dir)),
    gulp.src(COMPONENTS_IMAGES).pipe(gulp.dest(dir + "images")),
    preprocessCSS("web/pdf_viewer.css", "components", defines, true)
      .pipe(postcss([calc(), autoprefixer(AUTOPREFIXER_CONFIG)]))
      .pipe(gulp.dest(dir)),
  ]);
}
gulp.task(
  "components",
  gulp.series("buildnumber", function () {
    console.log();
    console.log("### Creating generic components");
    var defines = builder.merge(DEFINES, { COMPONENTS: true, GENERIC: true });
    return buildComponents(defines, COMPONENTS_DIR);
  })
);
gulp.task(
  "components-es5",
  gulp.series("buildnumber", function () {
    console.log();
    console.log("### Creating generic (ES5) components");
    var defines = builder.merge(DEFINES, {
      COMPONENTS: true,
      GENERIC: true,
      SKIP_BABEL: false,
    });
    return buildComponents(defines, COMPONENTS_ES5_DIR);
  })
);