perf: android proguard rules

[kraity]

What this PR does / why we need it?

生成jar包时增加Android混淆规则, 减少用户手动添加规则

Summary of your change

针对issues#2466中警告以及@JSONType和@JSONField注解引用

规则参考:
ProGuard Manual: Usage
gson.pro
katplus.pro

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

[wenshao]

请同时提交到android5和android8分支
https://github.com/alibaba/fastjson2/tree/android5
https://github.com/alibaba/fastjson2/tree/android8

[wenshao]

https://github.com/alibaba/fastjson2/releases/tag/2.0.50
2.0.50已发布，请用新版本