Filter comments by reactions

GitHub has only the Active and Resolved states for comment threads. This can be painful for complex PRs with large numbers of comments, where it would be more productive to track the status of thread in a finer grained way.

I sometimes use emoji reactions to simulate these states, e.g. using 👀 on the original comment to indicate pending (I'm now working on the change that addresses the thread, I haven't pushed it yet), or 👍 to indicate addressed (I pushed a fix, but original reviewer should check, decide if they agree that the problem is resolved, then hit Resolve on the comment thread).

As part of working with comments "tagged" in these ways, it would be nice to be able to filter the comments list, by whether certain reactions are present on the comments or not.

首先在仓库中定位 pull request 评论列表及其现有的 Active/Resolved 过滤入口。确定评论 reaction 的表示方式，然后定义对包含所选 reaction 的评论进行过滤；完成标准是评论列表可以按 reaction 是否存在进行过滤，且不会影响现有状态。