[Feature] 给插件提供 getTopActivity 相关api

[limao996]

What new features do you want? - 你想要什么新功能？

如题

This issue is unique - 这个issue是唯一的

• I have searched the issue tracker and did not find an issue describing my bug. - 我已经搜索问题追踪器并且没有发现相同的 issue。