introduced `messageContentForServerDB` function in reaction message spec. `messageContentForServerDB` returns the `targetMessageID` and the `reaction` as a stringified JSON object. The contents of this function are actually the same as `messageContentForClientDB`, so `messageContentForClientDB` can actually just call and return `messageContentForServerDB` for it's method now.
**UPDATE**
Based on some feedback I got on some subsequent diffs, I have removed `targetMessageID` from the `messageContent` in `messageContentForServerDB`. The big change with this update is that we should now be pulling `targetMessageID` directly from the server row instead of `content`. We are now separating the two messageContent functions since `rawMessageInfoFromClientDB` still needs `targetMessageID` from the client and `ClientDBMessageInfo` doesn't have a target_message_id field
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Depends on D5690
Linear Task: [[ https://linear.app/comm/issue/ENG-2245/setup-message-reaction-spec | ENG-2245 ]]