Discuss the full replacement of fastjson with fastjson v2 in Dubbo 3.1

The security issues of FastJson v1 continued, causing trouble for some users of Dubbo,
At present, FastJson has released the v2 version and solved the security risks in the v1 version.
v2: https://github.com/alibaba/fastjson2
In addition, v2 also brings performance improvements.
So I propose to replace the v1 version with the v2 version in the 3.1 version.
Reason for replacement in version 3.1: considering the compatibility issues of some users.