On https://github.com/mozilla/pdf.js/wiki/Required-Browser-Features we mention required browser features for PDF.js, but I have the feeling that not all of them are necessary nowadays since we moved to using more modern features over the years. Moreover, as indicated in https://github.com/mozilla/pdf.js/issues/11950#issuecomment-637149085, some features may be missing such as range requests or `async/await`.

In short, we should verify which are still necessary and update the wiki page and the automated feature detection if possible.
.src("external/dist/**/*", { base: "external/dist", stripBOM: false })
          .pipe(gulp.dest(DIST_DIR)),
        gulp.src(GENERIC_DIR + "LICENSE").pipe(gulp.dest(DIST_DIR)),
        gulp
          .src(GENERIC_DIR + "web/cmaps/**/*", { base: GENERIC_DIR + "web" })
          .pipe(gulp.dest(DIST_DIR)),
        gulp
          .src([
            GENERIC_DIR + "build/{pdf,pdf.worker,pdf.sandbox}.js",
            GENERIC_DIR + "build/{pdf,pdf.worker,pdf.sandbox}.js.map",
            SRC_DIR + "pdf.worker.entry.js",
          ])
          .pipe(gulp.dest(DIST_DIR + "build/")),
        gulp
          .src([
            GENERIC_LEGACY_DIR + "build/{pdf,pdf.worker,pdf.sandbox}.js",
            GENERIC_LEGACY_DIR + "build/{pdf,pdf.worker,pdf.sandbox}.js.map",
            SRC_DIR + "pdf.worker.entry.js",
          ])
          .pipe(gulp.dest(DIST_DIR + "legacy/build/")),
        gulp
          .src(MINIFIED_DIR + "build/pdf.js")
          .pipe(rename("pdf.min.js"))
          .pipe(gulp.dest(DIST_DIR + "build/")),
        gulp
          .src(MINIFIED_DIR + "build/pdf.worker.js")
          .pipe(rename("pdf.worker.min.js"))
          .pipe(gulp.dest(DIST_DIR + "build/")),
        gulp
          .src(MINIFIED_DIR + "build/pdf.sandbox.js")