[BUG] Exception on parsing object key with emoji and escape character

### Problem
Exception on parsing of JSON object with emoji and escape character in key

### Unit test

```java
Map<String, String> map = Map.of("\uD83D\uDE07\\", "");
byte[] jsonBytes = JSON.toJSONBytes(map, StandardCharsets.UTF_8);
assertEquals(map, JSON.parseObject(jsonBytes, Map.class));
```

Now this code throws `com.alibaba.fastjson2.JSONException: malformed input around byte 2`.