src: restore ASCII fast path in EncodeValidUtf8

Author: araujogui

src/string_bytes.cc

@@ -559,6 +559,9 @@ MaybeLocal<Value> StringBytes::EncodeValidUtf8(Isolate* isolate,
                                                const char* buf,
                                                size_t buflen) {
   buflen = keep_buflen_in_range(buflen);
+  if (!simdutf::validate_ascii_with_errors(buf, buflen).error) {
+    return ExternOneByteString::NewFromCopy(isolate, buf, buflen);
+  }
   if (buflen >= 32) return EncodeValidNonAsciiUtf8(isolate, buf, buflen);
   Local<String> str;
   if (!String::NewFromUtf8(isolate, buf, v8::NewStringType::kNormal, buflen)