Each message on the client needs to be aware if it's pinned or not - the best way I found to do this is in chat-selectors when we compose ChatMessageInfoItem. I purposely didn't include isPinned in RobotextChatMessageInfoItem since robotext messages cannot be pinned.
My main reference was @ginsu's reaction stack for this from D5811. I created a separate for (...) loop to avoid creating conditional checks in the one used for reactions, but if it'll be better to merge the two and perform different actions based on messageInfo.type, I can do that as well.
Linear: https://linear.app/comm/issue/ENG-3392/include-an-ispinned-flag-in-chatmessageinfoitem
Depends on D7148