fastjson1下时间序列化JSON.toJSONString（）时间转为时间戳[BUG]

原fastjson 1.*版本 JSON.toJSONString（） ，JSONObject.toJSONString（)等方法对于时间类型默认转成 yyyy-MM-dd hh:mm:ss格式
切换fastjson2.*版本，时间类型转成时间戳

Start by reproducing the difference between fastjson 1.* and fastjson2.* with JSON.toJSONString() and JSONObject.toJSONString() on a time value. Compare the serialized output with the prior yyyy-MM-dd hh:mm:ss format; the issue is done when the intended time representation is restored or the behavior is otherwise clarified.

Written by the indexing model from the issue text.